Background

Although chemotherapy and radiotherapy remain the mainstay of cancer treatment in developed countries, an increasing number of cancer patients are seeking benefits from complementary and alternative medicine. Surveys in the United States, Canada and Europe revealed that an average rate of 35% of cancer patients have utilized Chinese herbal medicine during their treatment [1]. Such prevalence of Chinese herbal medicine use in cancer patients from Asian countries is expected to be even higher [2, 3].

It is well-known that the concurrent use of Chinese and Western medicines can cause herb-drug interactions that lead to both beneficial and harmful health outcomes. To highlight, herb–drug interactions are not uncommon in cancer treatment and may affect the clinical efficacy or safety of the treatment. One study demonstrated that over half of the patients undergoing chemotherapy took herbal products, of whom 27% were found to be at risk of clinically significant interactions between chemotherapy drug and herbs. In another study, authors detected 120 possible herb–drug interactions in 149 patients who reported concurrent use of Chinese herbs with conventional anti-cancer drugs [4, 5]. As most chemotherapy drugs have a narrow therapeutic index, there is an urging need for clinicians and scientists to address the potential herb-drug interactions in oncology practice.

Among Chinese herbs, medicinal mushrooms have been used for a long time during the cancer treatment. Lingzhi (Reishi or Mannentake in Japanese) and Yunzhi (commonly known as Turkey tail) are common medicinal mushrooms that are readily available in Asian countries. They are believed to possess medicinal properties to treat cancers or relieve cancer-related symptoms [6]. The two mushrooms both belong to the Polyporaceae family and have similar characteristics based on Traditional Chinese Medicine theory including flavour and nature [7]. Despite their popular use in cancer patients, there are limited reports on the clinical outcomes from their herb-drug interactions during anti-cancer treatment.

Although systematic reviews and meta-analysis of Lingzhi and Yunzhi as an adjunct for cancer treatment have been performed [8,9,10], these reviews mostly focused on clinical outcomes with no mechanistic explanations for the potential beneficial or harmful interactions. By gathering both clinical and preclinical studies of this subject matter, the current systematic review aimed to evaluate the effects of the co-administration of cytotoxic drugs with the medicinal mushrooms, Lingzhi and Yunzhi. Specifically, we will identify potential pharmacokinetic and pharmacodynamic interactions between these medicinal mushrooms and chemotherapy drugs and discuss the implications of these interactions on the efficacy and safety of cancer treatment.

Methodology

Database search

A comprehensive search was conducted on the following databases: China Journal Net (1915 to June 2020), Wanfang Database (1990 to June 2020), and Chinese Biomedical Literature Database (1878 to June 2020). English databases included Allied and Complementary Medicine (1985 to June 2020), Embase (1910 to June 2020), Ovid MEDLINE® (1946 to June 2020), Ovid Nursing Database (1946 to June 2020), Ovid Emcare (1995 to June 2020), and Natural Medicines Comprehensive Database.

The combination of search terms included keywords for cytotoxic anticancer drugs and medicinal mushrooms as shown in Additional file 1: Table S1. The keywords used for cytotoxic drugs were based on the Hong Kong Hospital Authority Drug Formulary with no targeted therapy drugs included in the current review. In addition, chemoprotectants such as leucovorin and mesna were included in the current search. Besides the specific names of the cytotoxic drugs, general terms such as “cytotoxic drug” and “antineoplastic drug” were also included in the search to increase the coverage.

For the two medicinal mushrooms, Chinese name, English name, Pinyin and Latin name of them together with the names of their active ingredients were incorporated in the search. For Lingzhi, keywords for search included Reishi, Mannentake, Lingzhi, Ganoderma lucidum, Ganoderma sinense, Ganoderic acid, Polysaccharide, 靈芝, 靈芝酸, and 多糖. For Yunzhi, Turkey Tail, Yunzhi, Coriolus versicolor, Trametes versicolor, Polyporus versicolor, Krestin (PSK), Polysaccharide, Polysaccharide peptide (PSP), 雲芝 and 多糖肽. General terms including “medicinal mushroom” was also utilized in the search for more comprehensive coverage.

Inclusion criteria

This review included clinical, animal and in-vitro studies that reported the concurrent use of any cytotoxic drug with the two medicinal mushroom(s). The name of drug used, dosage form and administration route should be specified. The mushroom(s) could exist in any formulation containing a raw or processed form of the mushroom(s) that included the extract of its (their) active phytochemical components. They could be used alone or with other herbs or ingredients in a composite formula. Clinical studies had to involve two groups of patients, a control group that received only the cytotoxic drug or the medicinal mushroom(s) (or the mushroom-containing herbal formula) and a co-administration group that received the cytotoxic drug together with the medicinal mushroom(s). If the control group also received medicinal mushrooms, there should be significant dosage differences of the mushrooms in the treatment group. The languages of the included articles were restricted to English, Chinese and Japanese.

Assessing the quality of clinical studies

The Jadad scale was used to assess the quality of the clinical studies. This is a 5-point scale evaluating randomization, blinding, and withdrawals or dropouts of the clinical trials [11].

Results and discussion

Results of the database search

Figure 1 summarizes the process of database searching and literature selection. The initial search identified 9712 studies. After screening their titles and abstracts, about 455 studies were included and subjected to further full-text inspection and verifications based on the inclusion criteria. In total, 213 studies were included in this review with 119 of them focused on Lingzhi, 93 of them on Yunzhi, and 1 on the combination of Lingzhi and Yunzhi. Other characteristics of the included studies including languages used, type of studies, type of the mushroom preparations, and country of the origin, type of cancer together with Jadad score of the included clinical studies were summarized in Additional file 1: Table S2 and distributions of the included cytotoxic drugs were shown Additional file 1: Figure S1. The detailed information on the 77 clinical studies and 137 preclinical studies were listed in Additional file 1: Tables S3, S4, respectively.

Fig. 1
figure 1

PRISMA flow chart of current database search and literature selection

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Interaction outcome

Pharmacokinetic interactions

In general, evidence on the pharmacokinetic interactions between Lingzhi or Yunzhi and cytotoxic drugs was scarce, except for the clinical pharmacokinetics interaction investigations between PSK and Tegafur as illustrated below.

Clinical studies on pharmacokinetic interaction

Of all the 213 studies included in this review, only two studies evaluated the clinical pharmacokinetic interactions between cytotoxic drugs and medicinal mushrooms. Both studies evaluated the interactions between PSK (Yunzhi) and Tegafur (tetrahydrofuryl-5-fluorouracil), the prodrug of cytotoxic drug 5-FU. The conversion of Tegafur to 5-FU is mediated primarily by the CYP2A6 enzyme. Only small or non-significant changes in the blood level of 5-FU and Tegafur was observed in most patients with up to 8–14 months PSK co-administration [12, 13].

Pre-clinical studies on pharmacokinetic interaction

Only two in-vitro studies included in the review evaluated the pharmacokinetic interactions between Lingzhi and cytotoxic drugs. Ganoderic polysaccharides were shown to increase the distribution of doxorubicin in drug-resistant cancer cell lines, while Ganoderic acid B was shown to reverse the resistance of hepatocellular carcinoma toward doxorubicin, paclitaxel, and vincristine but not cisplatin [14, 15]. Since doxorubicin, paclitaxel, and vincristine are substrates of P-glycoprotein, Lingzhi or its components were expected to modulate the P-gp mediated efflux of these cytotoxic drugs to increase their cell accumulation and reverse their resistance in the tumor cells [16].

For Yunzhi, consistent with clinical findings, an animal study showed that regardless of the administration route, PSK had no effect on the tissue level of 5-FU or its prodrug Tegafur in tumor-bearing mice [17]. In addition, another animal study showed that PSP could decrease cyclophosphamide clearance and increase the plasma half-life without affecting its distribution or protein binding. It was also found that a dose-dependent relationship existed between the systemic exposure of cyclophosphamide and acute rather than sub-chronic treatment with PSP [18].

Pharmacodynamic interaction

Tables 1 and 2 summarized the clinical and preclinical pharmacodynamic interactions between Lingzhi/Yunzhi and cytotoxic drugs, respectively. Outcomes on survival and quality of life, tumor inhibition and disease control rate, immune system and alleviation of the other adverse effects of cytotoxic drugs were further illustrated as follows.

Table 1 Pharmacodynamic interactions between medicinal mushrooms and cytotoxic drugs in clinical studies
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Table 2 Pharmacodynamic interactions between medicinal mushrooms and cytotoxic drugs in preclinical studies
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Effect on survival and quality of life

a. Clinical evidence

Both Lingzhi and Yunzhi showed survival benefits in clinical studies. In this review, Yunzhi showed more clinical evidence than Lingzhi on increase in the survival rate and prolongation of the survival time. Among the 21 clinical studies on Lingzhi, only three studies measured survival outcomes with two of them reported increase in survival rate [19,20,21]. The survival rate increased when herbal formulae containing Lingzhi were used together with chemotherapy regimens (including 5-FU, cisplatin, doxorubicin, mitomycin, or vincristine). Notably, 37 of the 56 clinical studies on Yunzhi evaluated survival outcomes, 36 of which used PSK and one used Yunzhi-containing herbal formula. Twenty-nine of the 37 studies showed survival benefits of Yunzhi when co-administered with cytotoxic drugs. Among these Yunzhi–drug combinations, more evidence of survival benefits was reported for combinations with 5-FU, mitomycin, and UFT or Tegafur [22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50], whereas no survival benefits were reported for the combination with leucovorin [51]. Most of the Japanese studies on Yunzhi showed survival benefits of 3 or 5 years in gastric and colorectal cancers, leading to the approval of PSK approved as an adjunct in cancer treatment in Japan.

In terms of quality of life, Lingzhi co-administration with cytotoxic drugs has more clinical evidence than that for Yunzhi. Among the 21 included studies for Lingzhi, 12 of them measured the quality of life of cancer patients, and all of them observed an improvement by the co-administration of Lingzhi with 5-FU, capecitabine, cisplatin, gemcitabine, leucovorin, oxaliplatin, paclitaxel, and vinorelbine. The improvement in the quality of life was mostly observed in lung cancer patients (8 of the 12 studies) [21, 52,53,54,55,56,57,58,59]. Among the included studies, only 5 of the 56 clinical studies on Yunzhi measured the quality of life of cancer patients after the co-administration of Yunzhi with various cytotoxic drugs (5-FU, cisplatin, carboplatin, capecitabine, cyclophosphamide, doxorubicin, etoposide, mitomycin, oxaliplatin, paclitaxel and UFT) and all of them showed improvement [48, 49, 60,61,62].

Overall, more clinical evidence was reported on the survival benefits for the co-administration of chemotherapy with Yunzhi specifically PSK especially in gastric and colorectal cancer, whereas more evidence was reported on the improvement in the quality of life for the co-administration of chemotherapy with Lingzhi, especially in lung cancer patients.

b. Preclinical evidence

Animal studies on the concurrent use of Lingzhi or Yunzhi with cytotoxic drugs also measured the survival outcomes and substantiated the findings of the above-mentioned clinical studies. With regard to Lingzhi, its survival benefits were also observed in animal studies when co-administered with 5-FU, carboplatin, cisplatin, and doxorubicin which also shown benefits in clinical studies [63,64,65,66]. With regard to Yunzhi, the survival rate or time of animals increased when it was co-administered with 5-FU, cyclophosphamide, etoposide, and mitomycin, which were consistent with the findings from clinical studies [67,68,69,70,71,72,73,74].

Effect on tumor inhibition and disease control rate

a. Clinical evidence

Most of the clinical studies identified in our review measured efficacy based on World Health Organization or the Response Evaluation Criteria in Solid Tumor (RECIST) [75]. The co-administration of Lingzhi with various cytotoxic drugs showed an increase in disease control rate or clinical efficacy via the reduction of tumor lesion size; these drugs include 5-FU, capecitabine, cisplatin, doxorubicin, gemcitabine, leucovorin, mitomycin, oxaliplatin, paclitaxel, and vincristine [19,20,21, 52,53,54,55,56, 59, 76,77,78]. In addition, co-administration of Lingzhi with 5-FU and cisplatin could further reduce the expressions of microRNA-21 (miR-21), endoglin, transforming growth factor (TGF)-β, and vascular endothelial growth factor (VEGF) [76].

The co-administration of Yunzhi with several cytotoxic drugs (carboplatin, capecitabine, cisplatin, cyclophosphamide, doxorubicin, etoposide, mercaptopurine, oxaliplatin and paclitaxel) showed increase in clinical efficacy [49, 62, 79, 80] and improvements in disease progression or control [48, 50]. Some Yunzhi–drug combinations (5-FU, carboplatin, cisplatin, cyclophosphamide, doxorubicin, etoposide and UFT) also reduced tumor recurrence [25, 38, 42, 44] and metastasis [49]. Lower level of markers for tumor cell division, proliferation and invasion were found when paclitaxel and carboplatin were used with PSP [62].

Notably, most studies showed an enhancement in the cytotoxicity toward tumor cells when cytotoxic drug were used with these two medicinal mushrooms, suggesting no disadvantage for the addition of mushrooms in chemotherapy regimens.

b. Preclinical and mechanistic evidence

Our review revealed that the mechanisms of interactions between Lingzhi or Yunzhi and cytotoxic drugs involve multiple targets, including genes, proteins, and signaling pathways, to synergistically increase the tumor-inhibitory effect. Most animal studies support the clinical findings above. For Lingzhi, increase in the tumor inhibition rate was also demonstrated in animal studies [81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98] and in-vitro studies [96,97,98,99,100,101,102,103,104,105,106,107,108,109,110]. Some animal studies also observed suppression of metastasis by the co-administration of Lingzhi with cyclophosphamide [90, 91]. Regarding Yunzhi, enhancement of the antitumor effects of cytotoxic drugs and reduction in metastasis by Yunzhi have also been demonstrated in animal studies [68,69,70,71, 73, 111,112,113,114,115,116,117] and in-vitro studies [18, 115, 117,118,119,120,121].

The effects of Lingzhi co-administered with cytotoxic drugs on tumor inhibition were multifaceted in both animal and in-vitro studies. Some combinations exert synergistic effect through induction of cell cycle arrest at different stages or increase the apoptotic rate [81, 89, 91, 96, 99,100,101,102, 122,123,124]. In addition, the enhancement of the antitumor effect was shown to be achieved via the inhibition of tumor cell angiogenesis [104] or increase in the reactive oxygen species production [124]. Various in-vitro studies have shown that Lingzhi could enhance the tumor-inhibitory effect by reversing resistance to cytotoxic drugs [14,15,16]

Lingzhi co-administration with cytotoxic drugs affects different pathways and cancer targets. In animal and in-vitro studies, various pathways related to cell cycle arrest, apoptosis, and angiogenesis were affected, including the Janus kinase/signal transducer and activator of transcription 3 (JAK–STAT3), the protein kinase B (Akt) [106, 123] and the Human epidermal growth factor receptor 2 (HER2) signaling pathway [96, 108], eventually affecting the apoptotic molecules, for example, by altering B-cell lymphoma (Bcl) and Bcl-2-associated X (Bax) [66, 81, 125], caspase 3 and 8 activation [81, 100, 107, 125], and Fas and Fas Ligand (Fasl) [104]. The expression of other target genes or proteins was also affected, such as aquaporin [125, 126], VEGF and basic fibroblast growth factor (bFGF) [104, 127], and tumor metastasis suppressor gene 1 (TMSG-1) protein [91], all of which increased tumor inhibition. Notably, a recent study found that such synergistic effect may be due to the inhibition of tumor metabolism via down-regulating Warburg-related proteins and restoration of the gut dysbiosis induced by paclitaxel [97]. Regarding the increasing evidence of microbiota involvement in chemotherapy outcomes, it is worth looking into interactions with other cytotoxic drugs on gut microbiome level.

For Yunzhi, both PSK and PSP were reported to further enhance the apoptotic activity when co-administered with docetaxel, doxorubicin and etoposide [114, 115, 120, 128]. Similar to cytotoxic drugs, Yunzhi and its components could also act on the (a) expression of cell cycle arrest and apoptosis related genes and proteins, including Fas and Fasl [113]; Bax, Bcl-2, and BH3 interacting-domain death agonist (Bid) [128,129,130]; nuclear factor-κB (NF-kB) [115, 117, 120]; cellular inhibitor of apoptosis protein 1 (cIAP-1) [120] and caspase-3 [113, 120] and (b) targets related to angiogenesis and cell invasion, including matrix metallopeptidase 9 (MMP-9) [115], leading to synergistic effect when they are used together.

Yunzhi could also enhance the cytotoxicity of anticancer drugs via other mechanisms, such as direct increase in the activity of cytotoxic and tumor-infiltrating lymphocytes, decrease in the activity of suppressor T cells [38, 70], and decrease and increase in superoxide dismutase (SOD) and lipid peroxide levels, respectively, in cancer cells [131]. In addition, PSK was shown to enhance the antitumor effect of 5-FU and Tegafur by downregulating the expression of dihydropyrimidine dehydrogenase messenger RNA (mRNA) [118], as well as docetaxel via the suppression of survivin expression activated by docetaxel [117].

Interaction on immune system

a. Clinical evidence

In clinical studies, Lingzhi co-administration with cytotoxic drugs generally relieved bone marrow suppression. The combinations alleviated the decrease in white blood cells (WBCs), including lymphocytes and neutrophils, caused by chemotherapy alone (5-FU, capecitabine, cisplatin, doxorubicin, gemcitabine, leucovorin, mitomycin, oxaliplatin, paclitaxel, and vinorelbine). The number of other blood cells, including red blood cells (RBCs), hemoglobin, and platelets was also increased by the combinations compared with chemotherapy alone [19,20,21, 52,53,54,55,56,57, 59, 77, 78, 132,133,134]. Specifically, some combinations alleviated the decrease in or induced an increase in some T cells (CD3+, CD4+, CD8+), CD4+/CD8+ ratio and natural killer (NK) cells [19, 20, 52,53,54,55, 59, 76,77,78, 132,133,134].

Co-administrations of Yunzhi with various cytotoxic drugs (capecitabine, mercaptopurine, oxaliplatin, and Tegafur) were also shown to reduce immunosuppression in clinical studies [47, 48, 50, 135]. Studies have shown a reversal of the decrease in WBCs, in particular, improvement of the increase in or alleviation of the decrease in T cells (CD3+, CD4+, CD8+), increase in the CD4+/CD8+ ratio, NK cell activity, and subsequent the production of immunoglobulins and interleukins (IL) [23, 38, 49, 60, 62, 68, 79, 80, 136,137,138,139,140,141,142,143,144]. Inhibition on other blood cells, such as platelets and hemoglobin by cytotoxic drugs were also alleviated by the co-administered Yunzhi [80, 136,137,138,139,140, 144].

b. Preclinical and mechanistic studies

Animal studies also showed alleviation in the WBCs decrease with the co-administration of Lingzhi and different cytotoxic drugs, particularly in T cells and NK cells [65, 66, 81, 83,84,85, 87, 89, 90, 125,126,127, 145,146,147,148,149,150,151,152,153,154,155,156,157,158, 163]. In addition, phagocytic activity and production of cytokines, including immunoglobulins, interferons (IFN), IL, and TGF, were shown to be restored [64, 81, 85, 88,89,90, 127, 146, 149,150,151, 153, 155, 156, 158,159,160,161,162, 165]. Suppression in the number of RBCs, platelets, and in hemoglobin was also found to be alleviated in animal studies [83, 84, 87, 150, 153, 156, 157, 163,164,165].

The co-administration of Yunzhi with cytotoxic drugs showed similar effects on immune function in animal studies as those observed in clinical studies. Immunosuppression was reduced, including alleviation of the decrease in WBCs, particularly B cell and T cells (CD3+ and CD4+); increase in the CD4+/CD8+ ratio, NK cells and phagocytic activity; and subsequent production of interleukins, immunoglobulins, and antibodies [69, 73, 111,112,113,114, 129, 130, 148, 166,167,168]. Inhibition on other blood cells, including hemoglobin, also was alleviated [69].

A complete understanding of the mechanisms and factors underlying the effects of the interaction of Lingzhi or Yunzhi with cytotoxic drugs on the immune system is still obscure. Multiple mechanisms may be involved, including upregulation of transcription factors such as T-box protein expressed in T cells (T-bet) and GATA-3, which modulate the T helper cell balance [169]; downregulation of Bax expression to reduce caspase 3 activity and T cell apoptosis [170]; and reduction of the expression of negative regulators/transcription factors of immune responses, including Forkhead box protein 3 (Foxp3) and programmed death 1 (PD-1) [171].

Alleviation of the other adverse effects of cytotoxic drugs

a. Clinical evidence

The co-administration of Lingzhi with some cytotoxic drugs (5-FU, capecitabine, cisplatin, doxorubicin, gemcitabine, leucovorin, mitomycin, oxaliplatin, and paclitaxel) was shown to reduce common adverse effects, such as reduction of gastrointestinal discomfort (nausea, vomiting, constipation, and diarrhea) and stomatitis [19, 53, 56, 59, 77, 78]. Specific adverse effect, such as nephrotoxicity [56] was also shown to be ameliorated.

In clinical studies on Yunzhi, the use of PSK and PSP with cytotoxic drugs (5-FU, capecitabine, mitomycin, oxaliplatin, and UFT) ameliorated the general adverse effects, such as gastrointestinal discomfort (nausea and vomiting, diarrhea, and constipation) [48, 61, 136], mucositis [48], and fatigue [136]. Specific adverse effects of cytotoxic drugs, including peripheral neuropathy [143], mutations [172], and hand-foot syndrome [48], were also reduced.

b. Preclinical and mechanistic evidence

The Lingzhi and cytotoxic drug combinations were also found to relieve some adverse effects in animal studies; for example, they reduced damage to different organs, including the intestine [162, 173], the kidney [64,65,66, 174,175,176,177,178,179,180], the liver [66, 86, 157, 164, 165], and the heart [157, 181, 182]; and their adverse effects, such as nausea and vomiting [147, 183, 184], mutation [185], and neural tube defects [186].

Some studies have evaluated the mechanism underlying the protective effects of the mushroom–drug combinations against chemotherapy-induced side effects. For example, the mechanism underlying the reduction of doxorubicin-induced myocardial damage was found to be via the modulation of cardiac enzymes and reduction of the oxidative stress (such as increase in glutathione S-transferase (GST) and glutathione peroxidase (GPx) levels) in myocardial cells by Lingzhi or Ganoderma polysaccharides [181, 182]. Similarly, Lingzhi and its polysaccharides likely increased renocortical antioxidant levels and relieved the oxidative stress, thereby ameliorating cisplatin-induced renal damage. Furthermore, Lingzhi reduced the occurrence of neural tube defects caused by retinoic acid by upregulating the transcription of cyclin-dependent kinase 4 (CDK4) mRNA and the expression of CDK4 and nestin in neural epithelia [186].

For Yunzhi animal studies, cisplatin-induced renal damage was reduced by decreasing blood urea nitrogen (BUN) and serum creatinine (Scr) levels [166]. In both animal and in-vitro studies, PSK reduced the mutagenicity of mitomycin by decreasing the frequency of sister chromatid exchange and micronuclei formation [187, 188].

In summary, the aforementioned outcomes suggest that medicinal mushrooms have great potential to ameliorate the adverse effects of chemotherapeutic drugs in clinical settings.

Other effects in pre-clinical studies

Several chemotherapy drugs are known to cause oxidative stress which damage tumor cells but concomitantly damage normal cells and produce adverse effects [189]. The co-administration of Lingzhi with cytotoxic drugs, including cisplatin, cyclophosphamide, doxorubicin, and methotrexate increased the total antioxidant capacity and levels of different antioxidant enzymes, including superoxide dismutase (SOD), glutathione, GPx, and catalase, and decreased malondialdehyde levels, thereby reducing the oxidative stress [64, 81, 150, 157, 162, 175,176,177,178,179,180,181,182, 190,191,192]. In an in-vitro study, the co-administration of Yunzhi with cisplatin prevented the decrease in SOD activity by mimicking it to protect normal healthy cells while selectively promoting the decrease in SOD activity and increase in lipid peroxide levels in cancer cells, both of which synergistically increased tumor inhibition while leaving normal cells unaffected [131]. However, these findings have not yet been substantiated in clinical settings.

Undesirable interaction outcome

Overall, there is no reported undesirable herb-drug interaction between Lingzhi or Yunzhi and cytotoxic drugs in our included studies. Although interaction between PSP and cyclophosphamide may potentially increase the systemic exposure of cyclophosphamide, it is not known whether it could lead to significant changes in clinical outcomes [193]. Since our findings indicated that Lingzhi/Yunzhi and their components may potentially affect pharmacokinetics of anticancer drug, further clinical pharmacokinetic studies are warranted to investigate the necessity for dose adjustment of anticancer drug in clinical practice.

Quality of clinical studies

The clinical studies on the concurrent use of Lingzhi or Yunzhi with cytotoxic drugs were rated using the Jadad scale. Overall, most of the clinical studies on the combined use of mushrooms and cytotoxic drugs were not of high quality, scoring mostly 0–3 points. Most of them did not adopt blinding measures, probably because it is not feasible to blind chemotherapy regimens and complex herbal therapies. In addition, many studies lacked comprehensive description of withdrawal and dropouts. Only half of the randomized studies provided details on their randomization methods. Similar to the findings from others on clinical trials with Chinese medicine [194], the trials involved in the current review were also with poor clinical trial design and insufficient reporting of studies. Although the SPIRIT 2013 and CONSORT 2010 guideline have been published with intent to improve the design and reporting of randomized controlled trials, they may not be completely applied to the trials of Chinese medicine formulas. Thus, a CONSORT 2010 extension and SPIRIT-TCM extension have been established in 2017 and 2018 respectively to meet the unique characteristics of Chinese medicine [195, 196], which could serve as the guidance for future clinical studies involved Chinese medicines.

Conclusion and implication for future study

The combination of Lingzhi and Yunzhi with cytotoxic anti-cancer drugs showed great potential in offering beneficial effects in clinical settings with no undesirable interactions reported so far. The survival benefits can be increased, especially for Lingzhi and the quality of life of cancer patients can be enhanced especially for Yunzhi. Both Lingzhi and Yunzhi showed synergistic effect on tumor inhibition with chemotherapy, reducing immunosuppression and alleviating general and specific chemotherapy related side effects.

Despite a relatively large number of clinical studies conducted, the quality of clinical studies included in this review remained not high, especially with lack of blinding and description of all withdrawals and dropouts. Trials based on guidance from CONSORT 2010 extension and SPIRIT-TCM extension are highly recommended in the future to ensure the higher quality of clinical trial on Chinese medicines. Pharmacokinetic effects of Lingzhi or Yunzhi on cytotoxic drugs were inconclusive. There was currently significantly lack of studies on pharmacokinetic herb-drug interactions as revealed above. Considering the narrow therapeutic index of many cytotoxic drugs, more clinical pharmacokinetic studies are warranted for their safe and effective use.

In recent years, there are revolutionary advancements in the oncology world that sees many new breakthrough treatments, including targeted therapies, immunotherapy as well as gene therapy. Future studies should identify potential synergistic and harmful interaction between Chinese Medicine and these advanced cancer therapies. With increasing number of studies on combined usage of Chinese and western medicine, future studies can harness modern techniques such as bioinformatics and data mining to identify patterns of herb–herb and drug-herb combinations, especially those show the strongest evidence for tumor inhibition. Moreover, considering the large population utilizing Chinese Medicine in Asian countries and increasing prevalence in Europe and US, future pharmacoepidemiology studies can be conducted to observe the clinical impact of integrative medicine among cancer patients in a real word setting, in particular long-term and delayed effect that cannot be revealed in ordinary clinical trial settings.