Introduction

Gastric cancer is still the most common cancer in Asia, including Korea, and a rapid increase in the number of gastric cancer survivors attracted attention to their long-term health problems and their need for proper management [1, 2]. Few studies have determined that bone loss after cancer therapy is more rapid, especially in the first year after gastrectomy, and about 50% of patients who underwent gastrectomy were diagnosed with osteoporosis within 10 years after index surgery [3, 4, 5]. The risk of osteoporotic fracture also higher compared with those of the general postmenopausal women or normal age-related osteoporosis in men. Several hypotheses including secondary hyperparathyroidism and gastric dumping have been suggested for postgastrectomy osteoporosis [6, 7].

Endoscopic submucosal dissection (ESD)/endoscopic submucosal resection (EMR) are widely accepted approaches to the therapy of early gastric cancer [8]. Recently, especially in Korea, approximately 50% of gastric cancer cases are diagnosed at their earliest stage because of the national screening programs and frequent opportunistic screening so there are many patients treated with ESD/EMR [6, 9]. However, the risk of osteoporotic fracture has not been compared and evaluated according to the type of surgery including ESD/EMR.

Evaluation of large datasets has been widely applied in various fields of medicine [10]. An example of such a dataset is insurance claim data, which has the advantage of containing information regarding a large number of registrants and their healthcare services although there is a lack of detailed medical information because the data were not generated for research purposes. Thus far, nationwide databases such as the Korea National Cancer Incidence Database (KNCIDB) built by the Korea Central Cancer Registry (KCCR) in Korea. The KNCIDB is a population-based cancer registry, wherein the annual cancer records are incorporated with death certificate information from Statistics Korea.

Herein, we evaluated the incidence of OF and the factors associated with fracture risk among gastric cancer survivors. The aim of the study was to investigate clinicopathological factors associated with osteoporosis after gastrectomy, to develop and validate a nomogram for predicting the incidence of osteoporosis after surgery for gastric cancer.

Materials and methods

Data source and linking

We used data from the Korean National Health Insurance Service (KNHIS) and Korea Central Cancer Registry(KCCR) for our analysis. All Koreans (97%) are covered by mandatory universal health insurance and KNHIS database includes all information regarding reimbursement for outpatient visits and hospital admissions. This information includes the involved medical diagnoses (based on the International Classification of Diseases 10th revision [ICD-10]), procedures, prescriptions, and costs incurred. It also collects information regarding the qualification of beneficiaries, including age, sex, monthly insurance premium (a proxy for household income status), and disability. It also contains the results of health check-up data because the KNHIS provides a biennial National Health Screening Program to all beneficiaries who are 40 years and older and all employees regardless of age.

The Korean Ministry of Health and Welfare started a nationwide registry (Korea Central Cancer Registry, KCCR) for collecting data on cancer incidences and providing insurance benefits for patients. All patients with cancer in Korea were registered in the KCCR with diagnoses based on the ICD-10. Since 1999, population-based cancer incidence data have been produced systematically, and the KCCR data from 1999 to 2002 have been published in the Cancer Incidence in Five Continents. Vol. 9, which reflects the completeness and validity of the dataset. The cancers recorded in the KCCR were classified based on the International Classification of Disease for Oncology, 3rd edition (ICD-O-3). The KCCR data includes patient information (sex and age at the time of diagnosis), cancer information (date of diagnosis, tumor site, histology type, and Surveillance, Epidemiology, and End Results [SEER] summary stage), and first-line treatment information (surgery, chemotherapy, radiothereapy [RT], immunotherapy, and hormone therapy). For the multiple primary rules, we used the definition from the International Agency for Research on Cancer. These two databases are linked by linking the patient’s personal information (name, date of birth, gender).

The present study complied with the Declaration of Helsinki. This study was approved by the institutional review board of the SNUBH Hospital (IRB No. C2014086(1282). Written informed consent from individual subjects was waived.

Study population: identification of eligible patient

We found 294,033 patients who underwent gastrectomy for stomach cancer by combining ICD-10 a diagnosis of stomach cancer (C160–C169) and procedure codes (Supplementary Digital Content 1) between January 1, 2008, and December 31, with a wash-out period of 1 year (2007).

From the Health Insurance Review and Assessment Service database, a total of 175,427 patients were selected after linking the patient’s personal information (name, date of birth, gender). Patients were excluded if they had a diagnosis of another cancer or metastasis during follow-up (n = 5670), a history of medication for RA or glucocorticoids (n = 11,660), were treated with medications for osteoporosis (bisphosphonate or selective estrogen receptor modulators, which were available at the time of the study) (n = 4170), or had a previous admission for osteoporotic fracture (n = 2353) or died within 6 months after surgery (n = 1410), or two or more conditions overlap (n = 8903). Ultimately, a total of 85,124 gastric cancer survivors from 2008 to 2016 were included. The type of surgery was classified as total gastrectomy (TG, n = 14,428)/subtotal gastrectomy (SG, n = 52,572)/endoscopic mucosal resection and endoscopic mucosal resection (ESD/EMR, n = 18,125). We excluded all pathological fractures due to metastasis because the claim code for procedures of pathologic fracture is different from the code for the treatment of osteoporotic fractures.

Outcome measures

The primary outcome was the incidence of osteoporotic fracture. The site of osteoporotic fractures included spine, hip, wrist, and shoulder. Fractures related to osteoporosis were combining the ICD code of fractures and procedure codes, as previously described [27, 28] (Supplementary Digital Content 2). To assess risk factors associated with fracture, following variables were investigated; patient age at the time of the index gastrectomy, sex, types of surgery, income level (decile distribution), place of residence (urban or rural), SEER staging (localized, regional, distant, unknown), Charlson comorbidity index (CCI).

The participants were followed from the index date to the first occurrence of fracture, death or censored date, or the end of the study period (December 31, 2016).

Statistical analysis

Descriptive statistics were used to determine the baseline characteristics of the study population. Kaplan–Meier curves were used to demonstrate the cumulative incidence of fracture over time. Cox proportional hazards regression analysis was used to compare the relative risk of fracture among gastric cancer survivors. The factors associated with osteoporotic fracture in gastric cancer survivors were analyzed using the multivariate cox proportional hazards regression model. The assumption of proportional hazards was assessed before all analyses. All analyses were performed using STATA (version 14.0; Stata Corporation, College Station, TX, USA). We examined cumulative incidence using Kaplan–Meier survivor analysis and cox proportional hazards regression analysis was used to determine the risk factor of OF in gastric cancer survivors.

Results

Characteristics of the study population

Clinical characteristics of the study survivors who underwent gastric cancer surgery are summarized in Table 1. The cohort comprised 64,105 men and 21,019 women with a median age of 53.5 years (range 31–92 years). Surgical treatment comprised total gastrectomy in 14,428 patients (16.9%), subtotal gastrectomy in 52,572 patients (61.7%) and 18,124 patients (21.3%). Patients with ESD/EMR were more frequently males, were younger, had lower CCI, and a history of localized stage of cancer compared with patients who underwent gastrectomy.

Table 1 General and clinical characteristics of gastric cancer patients according to Surgery type (2008–2016)
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Incidence of osteoporotic fractures

Of the 85,124 subjects identified in the total group, 2645 (3.1%) gastric cancer survivors experienced an osteoporotic fracture over a median of 4.5 years of follow-up. Of all 2645 fractures, wrist fractures were the most common site (n = 1182, 44.7%) and 1,018 spine fractures (38.4%), 515 hip fractures (19.4%), and 104 shoulder fractures (3.9%), were identified (Table 2).

Table 2 Incidence rate of osteoporotic fracture in gastric cancer patients accordinging to surgery type
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The incidence rate per 100,000 patient year was 2.6 in TG, 2.1 in SG, 1.8 in ESD/EMR group. The cumulative incidence rate was 2.3% at 3 years, 4.0% at 5 years, and 5.8% at 7 years in gastrectomy group, and 1.8% at 3 years, 3.3% at 5 years, and 4.9% at 7 years postoperatively in ESD/EMR group postoperatively (Table 3). Total gastrectomy had an elevated risk of OF compared to patients who underwent SG (hazard ratio [HR] 1.75, 95% 95% confidence interval [CI] 1.57–1.94), and ESD/EMR (HR 2.23, 95% CI 2.14–2.32) and similar patterns were observed in each site except humerus (Fig. 1).

Table 3 Univariate and multivariate cox proportional hazard ratio model for risk of osteoporotic fracture
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Fig. 1
figure 1

Kaplan–Meier curves for incidence of osteoporotic fracture according to the type of surgery in gastric cancer survivals. ESD/EMR, Endoscopic submucosal dissection/endoscopic mucosal resection, A all fractures. B wrist, C spine, D hip € shoulder

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The risk of osteoporotic fracture in gastric cancer survivors

Multivariate analysis of the screening subset showed the following factors were significantly associated with increased fracture risk: age (hazard ratio [HR] 1.06, 95% CI 1.058–1.062); female sex (HR 2.08, 95% CI 1.92–2.26); rural residence (HR 2.61, 95% CI 1.98–3.44); SEER stage (HR 1.25, 95% CI 1.14–1.37); and mCCI but radiation therapy and chemotherapy were not the risk factors (Table 3).

Cox proportional hazard ratio model after adjusting risk factors revealed that TG elevated risk of OF compared to patients who underwent EMR/ESD in localized SEER state (adjusted hazard ratio [aHR] 1.21, CI 1.07–1.37), aged > 60 (aHR 1.26, 95% CI 1.09–1.45), men (aHR 1.45, 95% CI 1.24–1.70), CCI > 4 (aHR 1.29, 95% CI 1.12–1.48) (Table 4).

Table 4 Cox proportional hazard ratio model for risk of osteoporotic fracture according to SEER stage, age group, sex, and mCCI
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Discussion

To the best of our knowledge, our study is the first to compare the fracture risk in gastric cancer survivors according to the treatment modality (gastrectomy vs endoscopic treatment). Currently, EMR/ESD is becoming more widely accepted, enabling detection and curative resection of early esophageal cancer, and increasing the number of long-term gastric cancer survivors [11]. Considering high prevalence of osteoporosis in long-term survivors of gastric cancer, more attention is required for follow-up management [12]. Although it was pointed out that the risk of osteoporosis may be related to the gastrectomy itself rather than the surgical method, these studies were limited to gastrectomy [13]. We postulated that endoscopic treatment might lower the complications because endoscopic resection could preserve the function of the stomach more than gastrectomy.

Our study demonstrated that patients who underwent gastrectomy had 1.61 times increased risk of fracture than did endoscopic treatment. Two main pathogenesis for increased risk of osteoporotic fractures are the followings. (1) Calcium and vitamin D deficiency and subsequent secondary hyperparathyroidism, (2) weight loss/anemia after gastrectomy [14, 15]. Gastric dumping and decreased acid secretion after gastric surgery may be greater in patients with open surgery than that those with endoscopic treatment [16, 17, 18]. The second pathophysiological mechanism can also be proportional, in that the wider extent of resected stomach the more weight is lost [19, 20]. Other previous studies demonstrated that the extent of gastric surgery and the change in bone metabolism appears to be proportional [5, 16]. Another longitudinal study with 56 early-stage gastric cancer survivors study confirmed that decrease in BMD, which was greater in the gastrectomy group than in the endoscopic treatment group [6].

The gastrectomy significantly increased the risk of OF in male patient (HR 1.65) but not in female (HR 1.02). Previous studies have shown that male patients who underwent gastrectomy are at an increased risk of osteoporotic fractures, particularly in the years following the surgery, so a higher incidence of osteoporosis and osteoporotic fracture had been reported compared to the general male population. According to a prospective study in men only, BMD and T score significantly decreased as early as 1 year after gastrectomy (changes from the baseline BMD were − 4.03%), and the proportion of patients with osteoporosis 1 year after gastrectomy was as high as 53.9% [21]. Other previous cross-sectional studies reported that the vertebral BMD in normal adult men decreased linearly by 0.0021 g/cm2 per year and by 5% in 10 years and a low preoperative BMI might be a predictor of osteoporosis and related fractures after gastric cancer surgery [22, 23, 24]. However, men are less likely than women to be screened for osteoporosis and to receive treatment for osteoporotic fractures, even gastric cancer is more frequent in males [25, 26, 27]. Thus, educating gastric cancer survivors, about the importance of regular screening and developing a strategies for osteoporosis in gastric cancer survivors, including men would be an important step towards improving the early detection and management of osteoporosis in these population.

The incidences of osteoporotic fracture at sites are consistent with the previous findings showing that fractures occur in the order of risk for fractures common in osteoporosis: forearm, spine, hip, and shoulder [28]. Also, we found that gastrectomy, age, female, advanced stage of cancer, comorbidities were clinical predictors of elevated fracture risk. Some previous studies indicated that there was no difference between osteoporosis rates between early and advanced gastric cancer so gastrectomy itself affects BMD rather than the reconstruction or surgery method [13, 29]. However, the preservation of the stomach and the change in bone metabolism appear to be proportional, so surgical methods for gastric cancer might be a cautionary factor for postoperative bone metabolism [5, 30, 31, 32].

The Fracture Risk Assessment Tool (FRAX), released by the World Health Organization in 2008, is a major achievement in helping determine which patients may be candidates for pharmacological therapy for osteoporosis. We acknowledge that the impact of gastrectomy on bone mineral density can vary depending on the extent of the surgery but also the patient’s individual risk factors. However, FRAX did not adopts any previous cancer history for calculating fracture risk, the risk of major osteoporotic fracture might be underestimated among gastric cancer survivors. A meta-analysis from 19 cohort studies have demonstrated that osteoporosis and fractures occur in the relatively early phase (within at least 5 years) after gastrectomy [12]. Another long-term follow-up observational study found that fracture mostly occurred within the first 6 postoperative years, but the cumulative incidence continued to increase afterwards [7]. Therefore, an evaluation of osteoporosis including BMD and laboratory tests such as calcium, phosphorus, 25(OH)D, PTH and bone turnover markers should be assessed much earlier than the general population. In addition, detailed approaches and risk factor stratification for gastric cancer survivors, such as FRAX which predicts fracture risk in the general population, are needed.

This study has several limitations. First, the general population was not included so we could not evaluate fracture risk in patients who underwent endoscopic treatment compared with that of matched controls. Second, some factors that have been shown to increase the risk of osteoporosis in other studies, including diabetes mellitus and smoking history, were not evaluated as data from the health-promotion center included information on co-morbidities based on a survey. We feel that most patients might be under the acute stage, because they got cured without aggressive physical therapy nor manipulation under anesthesia.

Conclusion

On the basis of our study, the risk of osteoporotic fracture was greater in the gastrectomy group than in the endoscopic treatment group and advanced stage of cancer, comorbidities were associated with osteoporotic fracture. Further research is required to establish screening guidelines for bone health according to cancer stage and surgical treatment, and then stage approach can be recommended.