Male breast cancer: finding the way in this uncommon path

Male breast cancer (BC) is a rare disease and accounts for less than 1% of all BCs. Knowledge of this disease is limited and mainly derives from small single-institution retrospective studies with contradictory results. The management of male patients with BC is generalised from the management of BC in women. However, evidence is growing that the biology of male BC differs at least partly from female patients with BC. An analysis of the Surveillance, Epidemiology, and End Results (SEER) registry containing a total of 5494 men and 8 35 000 women diagnosed with BC between 1973 and 2005 showed that advanced stage-related tumour characteristics (eg, tumour size >2 cm and positive axillary lymph nodes) were more common in men compared with women. In contrast, negative biology-related prognostic factors like hormone receptor (HR) negativity and high tumour grade were more often found among women. While 23% of the female breast tumours were oestrogen receptor negative, this was only the case for 7.6% of the male tumours.1 Inconsistencies have also been reported regarding the HER2 status of male BC. A combined analysis of nearly 60 studies on male BC in 2010 reported a higher rate of HER2 positivity in men compared with women with BC (34% and 25%, respectively),2 which is in contrast to the SEER data and other recent studies.3 4 However, the combination of data from different studies with different methodologies and cut-offs for HER2 positivity must be interpreted with caution. In this edition, Xing-Fei Yu et al report the results of a retrospective study of 134 cases of male BC treated at Zhejiang Hospital in China between 1990 and 2008. Based on the latest 2013 American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) guidelines for ER/progesterone receptor (PR) and HER2 testing, their results were consistent with the SEER data and other recent studies showing that most male tumours are ER+ and that HER2 positivity seems to be less common in men than in women with BC. The authors also evaluated the effect of adjuvant chemotherapy in male BC. The majority of patients (58.21%) received adjuvant chemotherapy. Even if the disease-free survival and overall survival rates were the same for patients with and without adjuvant chemotherapy, the authors suggest that chemotherapy might have a positive impact on OS as patients undergoing chemotherapy had a more advanced disease and displayed more aggressive biology-related characteristics like HR negativity and HER2 positivity. This article opens the door for a current and important discussion in BC: Is male BC similar to female BC and if so, can the current available treatments used to treat women with BC be safely extrapolated to men with BC? Trying to address these questions, an international consortium, coordinated by the European Organisation for Research and Treatment of Cancer and Translational Breast Cancer Research Consortium under the Breast International Group and the North American Breast Cancer Group network, was created to better characterise and manage male BC. First results of part 1, a retrospective analysis of clinical data including a central pathology review of tumour specimens in order to overcome difficulties seen in individual studies with different methodologies, were presented at the San Antonio Breast Cancer Symposium in 2014 and highlighted important differences between male and female BC. Among 1473 male patients with BC, more than half of the cases were ER positive, PR positive, androgen receptor positive and were classified as luminal A-like subtype (58%). Interestingly, only 5% was HER2 positive and 1% was triple negative, which is far less common than the reported rates in female BC.5 Furthermore, the association between different histological features and outcomes seems to differ between men and women: unlike in female BC where the histological grade is associated with poorer survival, this association was not found in a retrospective analysis in male BC.6 Editorial