Breast cancer (BC) is remarkably heterogeneous with respect to genotypic, phenotypic and behavioural characteristics and subsequent response to treatment. With an increasing number of treatment options available for BC patients, deciding the most appropriate choice remains challenging. However, accurate personalised BC treatment requires robust and accurate risk stratification based on both outcome prediction and biology of tumours [1], combined with therapeutic modality response and resistance assessment.
The Nottingham prognostic index (NPI) [2–5] is based on histopathological factors (tumour size, lymph node stage and tumour grade) and is used to stratify BC patients with operable early-stage primary BC into prognostic groups. The NPI accuracy has been confirmed using long-term patient follow-up [2], validated in large independent multi-centre studies [3, 6], revised in order to stratify patients into additional prognostic groups [7], and is currently adopted in clinical practice in the UK and other parts of Europe and Australia. However, the NPI does not consider the biological heterogeneity of BC and it therefore needs further refinement to support a more sophisticated personalised management of patients.
We have therefore developed a biomarker-based prognostic index, Nottingham prognostic index plus (NPI+) [8], using a large well-characterised series of early-stage BC. NPI+ is based on the well-established clinicopathologic variables used in the NPI but has been refined to integrate with tumour biology. It utilises routine formalin-fixed clinical samples and immunohistochemistry (IHC) thus providing an easy adoption into the current international clinical practice. NPI+ is based on a two-tier evaluation; initially the biological class of the tumour is determined and is then combined with clinicopathologic prognostic variables resulting in bespoke NPI-like formulae for each biological class [8–11]. NPI+ is able to assist in predicting long-term patient survival and to support clinical decision making in BC management [8]. Breast tumours are classified into seven core BC biological classes by the evaluation and combination of 10 BC-related biomarkers using IHC [12]. The molecular classes identified are three luminal classes (Luminal A, N and B), two basal classes (Basal—p53 altered and Basal—p53 normal) and two HER2+ classes (HER2+/ER+ and HER2+/ER−). Each biological class is further stratified using a set of well-defined prognostic clinicopathologic variables which are combined in tailored formulae to stratify each individual molecular class into several prognostic subgroups (NPI+ Groups) which are superior to the classic NPI [8]. Recently, we have further refined the NPI+ algorithms and validated the NPI+ in an independent series of primary BC confirming its reproducibility in providing accurate risk stratification allowing improved individualised clinical decision making for BC [13].
In this study, we aimed to determine the applicability of NPI+ to predict risk of distant metastases in two series of clinically annotated early-stage primary invasive BC.
Patients and laboratory methods
Nottingham series
A series of 1073 patients from the Nottingham-Tenovus Primary Breast Carcinoma Series, aged 70 years or less, presenting with primary operable (stages I, II and IIIa) invasive BC between 1986 and 1998 were previously used to develop the NPI+ [8–11]. This is a well-characterised consecutive series of patients who were uniformly treated according to locally agreed clinical protocols (Abd El-Rehim et al. [9]). All tumours were less than 5 cm diameter on clinical/pre-operative measurement and/or on operative histology (T1 and T2). Women aged over 70 years were not included because of the increased confounding effect of comorbidities/death from other causes and because the primary treatment protocols for elderly patients often differed from those for younger women. Adjuvant systemic therapies were offered according to the Nottingham prognostic index (NPI) and hormone receptor (HR) status [2, 7]. Patients in the Moderate I group (NPI 3.41–4.4) with HR-positive tumours were offered hormonal therapy. Patients in the Moderate II (NPI 4.41–5.4) and Poor (NPI > 5.41) groups received hormone therapy for HR-positive tumours and cytotoxic therapy (classical cyclophosphamide, methotrexate and 5-fluorouracil (CMF)) for HR-negative tumours and if the patient was fit enough to tolerate chemotherapy. Hormonal therapy was given to 396 patients (40.3 %), chemotherapy to 213 (19.9 %). Only 19 patients (1.9 %) received a combination of chemotherapy and endocrine therapy (Table 1). Data relating to survival were collated in a prospective manner for those patients presenting after 1989 only. All samples from Nottingham used in this study were pseudo-anonymised and collected prior to 2006 and therefore under the Human Tissue Act informed patient consent was not needed. Release of data was also pseudo-anonymised as per Human Tissue Act regulations.
Table 1 Pathological characteristics of the Nottingham and Budapest series
Budapest series
This series comprised 368 screen detected and symptomatic consecutive cases diagnosed with primary breast cancer between 1999 and 2002 and operated at the Buda MÁV hospital, Budapest, Hungary. A total of 251 cases were assembled in TMAs; the remaining cases were not included due to technical reasons or lack of relevant data. The age range of patients was 30–88 years, and pathological size was 14 cm and less. All pT stages and inflammatory breast cancers were included. A total of 42.4 % of the patients received the classical Bonadonna scheme (CMF), at the time the standard chemotherapy, unless comorbidities or advanced age permitted. Patients with hormone receptor positive invasive tumours were treated with Tamoxifen. According to the radiation therapy recommendations valid at the time, loco-regional radiation therapy was added to the postoperative treatment in cases of breast conservation and in those patients undergoing mastectomy who had 4 or more axillary lymph node metastases (134 patients, 57.4 %). Pathological features were retrieved from the pathology reports and slides were reviewed. Treatment data were collected from patients’ medical records. The evaluation was approved by the Institutional Review Board of Semmelweis University (IKEB, #185/2007). No informed consent was required by the Institutional Ethical Committee.
Pathological characteristics of both series are summarised in Table 1. Metastases-free survival (MFS) is defined as the interval (in months) between the primary surgery and occurrence of metastases being scored as an event. Metastases did not include local (ipsilateral) or regional recurrences, contralateral breast cancer. Lymph node metastases did not include regional lymph nodes. Patients who did not have metastatic disease were censored at the time of last follow-up.
This study was approved by the Nottingham Research Ethics Committee 2 under the title 'Development of a molecular genetic classification of breast cancer’.
Determination of NPI+ biological class
Immunohistochemical reactivity for the NPI+ biomarkers in the Nottingham series was previously determined using standard immunocytochemical techniques on tumour samples prepared as tissue microarrays (TMAs) [9]. The NPI+ biomarkers used for classification were oestrogen receptor (ER), progesterone receptor (PgR), cytokeratin (CK) 5/6, CK7/8, epidermal growth factor receptor (EGFR; HER1), c-erbB2 (HER2), c-erbB3 (HER3), c-erbB4 (HER4), p53, and Mucin 1 [11]. TMAs of the Budapest series were additionally stained for the NPI+ biomarkers using the same procedures as previously described [9, 11]. The Budapest TMAs consisted of 2 mm tissue cores and were produced as previously described [14]. Each tumour was represented by two cores. Levels of immunohistochemical reactivity were determined by microscopic assessment using the modified Histochemical score (H score), giving a semi-quantitative assessment of both the intensity of staining and the percentage of positive cells (values between 0 and 300) [15, 16]. For HER2, the American Society of Clinical Oncology/College of American Pathologists Guidelines Recommendations for HER2 Testing in Breast Cancer were used for assessment [17]. Equivocal (2+) HER2+ cases were confirmed by FISH/CISH [18]. The Reporting Recommendations for Tumour Marker Prognostic Studies (REMARK) criteria [19] were followed.
Determination of NPI+ score
For biological classification, a fuzzy logic rule-based method algorithm was used where the cut-offs for each biomarker were previously determined [12]. In particular, the median value of markers was used for ER, PgR, CK7/8, HER3, HER4 and MUC1. The expertise values were used for those markers which had a median equal to zero and for those where clinicians were sure about the value to consider (CK5/6, EGFR, p53 and HER2).
The NPI+ prognostic groups were calculated using bespoke NPI-like formulae, previously developed for each NPI+ biological class of the Nottingham series, utilising the existing available clinicopathological parameters [8]. Briefly, these were established by utilisation of the Beta values generated by Cox regression analysis in predicting breast cancer-specific survival of the well-established histopathologic prognostic factors. These formulae were initially derived from the Biological Classes in Green et al. [11] and were subsequently refined using the improved biological classification used in Soria et al. [12] consisting of number of positive nodes, pathological tumour size, stage, tubule formation, nuclear pleomorphism and mitotic counts. These were identified as the most significant variables in the Nottingham series impacting on survival, according to their Beta value in Cox regression indicating the magnitude of the influence of the hazard. The Nottingham series was split into the NPI+ biological classes, and Cox regression analyses were performed independently for each class to identify the most significant clinicopathological prognostic factors and their beta value in the context of the individual classes. NPI+ Prognostic Groups for the Budapest series were assigned using the categorical cut-points previously derived from the Nottingham series in each of the NPI+ biological classes [8]. For this purpose, the original pathology assessments on full-face sections for the histopathologic parameters were utilised.
Statistical analysis
The association between BC classes and both histopathological and clinical characteristics was assessed using Cramer’s V [20] to produce p values. MFS differences between NPI+ biological classes and NPI+ Groups were determined using Kaplan–Meier curves using Log Rank. A p < 0.01 was considered significant with Bonferroni adjustment for multiple testing.