A hierarchical approach to combine histological grade and immunohistochemical factors to identify high-risk luminal breast cancers

Background: The luminal subtype accounts for similar to 70% of newly diagnosed breast cancer patients. Although it has a better prognosis, approximately 30% of them develop a late relapse. Identifying those patients is of interest to improve treatment decisions. Methods: A retrospective observational, single-centre study based on data from medical records of 572 non-metastatic (I-III) invasive ductal breast carcinoma patients, 448 with luminal tumours and 124 with triple-negative tumours. Kaplan-Meier, Cox regression and time-dependent Cox regression were carried out to obtain the prognosis value of risk factors. Results: During a median observation of 5.5 years, 105 distant metastasis events and 105 all-cause deaths were observed. In addition to known clinicopathological factors (i.e., age, tumour size and lymph node metastasis), the high semi-quantitative expression of both hormone receptors was associated with distant metastasis-free survival (DMFS) (adjusted hazard ratio (HaR): 0.524 (0.316-0.867), p = 0.012) and overall survival (OS) (adjusted HaR: 0.486 (0.286-0.827), p = 0.008). The stratified analysis made it possible to identify risk modification factors. Subsequent stratification by histological grade, Ki-67 and semi-quantitative PR expression or, mainly, the composite semi-quantitative expression of hormone receptors (cHR) enabled the identification of luminal breast cancer patients of adjuvant schema at higher risk for metastasis and death. However, initial analyses including patients of neoadjuvant therapy pointed to a path of subsequent stratification by cHR and histological grade, also enabling grouping of luminal breast cancer patients with similar prognosis for DMFS (cHR <= 4+ G2 or G3 versus triple-negative, adjusted HaR: 0.703 (0.415-1.189), p = 0.189) and OS (cHR <= 4+ G2 or G3 versus triple-negative, adjusted HaR: 0.662 (0.403-1.088), p = 0.104). Conclusion: The semi-quantitative expression of both cHR, Ki-67 proliferation index and histological grade can identify luminal breast cancer patients at greater risk of developing metastasis and death when combined in a hierarchical fashion, and could be useful for a better prognosis stratification in services from low-and middle-income countries.