A comprehensive characterisation of tumour subtypes in male patients with breast cancer based on receptor expression together with outcomes based on these subtypes was presented during the Genomics and Proteomic Analysis of Breast Cancer portion of a Poster Walk at the IMPAKT Breast Cancer Conference held 7–9 May 2015 in Brussels, Belgium.
Rajesh Yadav and colleagues from the Beaumont Health System, Royal Oak, USA, noted that male breast cancer is a rare disease with an incidence of approximately 1% among all breast cancers, which possibly accounts for the current paucity of molecular data for this cohort.
The investigators used case data from 922 patients with known receptor subtypes included in the National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) programme for all male breast cancers diagnosed since 2010.
The majority of tumours from male breast cancer patients express a hormone receptor
Analysis of these data revealed that 757 (82%) of patients had tumours that were hormone receptor positive and HER2 receptor negative (HR+/HER2-), 135 (15%) patients were hormone receptor and HER2 receptor positive (HR+/HER2+), 11 (1%) patients were hormone receptor negative and HER2 positive (HR-/HER2+), and 19(2%) patients had triple-negative (HR-/HER2-) breast cancers.
The investigators found that triple-negative breast cancers were diagnosed in patients at a significantly younger age compared to hormone receptor positive breast cancers.
Racial composition and histology were similar across the different subtypes of male breast cancers. However, differences across subtypes in overall stage (p = 0.052) and nodal status (p = 0.051) were noted.
According to the authors, significant differences between the groups in histologic grade, tumour stage and metastasis status at diagnosis were found.
Poorer one-year survival rates seen with triple negative subtype
An evaluation of one-year overall survival (OS) rates showed patients with tumours expressing at least one receptor fared far better than those with triple-negative tumours.
One-year OS rates in male breast cancer patients were 95% overall; a breakdown by subtype showed a rate of 96.7% in the HR+/HER2- subtype, 90.0% in the HR-/HER2+ subtype and 89.9% in the HR+/HER2+ subtype compared to 67.9% in the HR-/HER2- tumour subtype.
A similar pattern was seen for one-year cause specific survival where rates were 96.6% overall, 98.2% for the HR+/HER2- subtype, 90.0% in the HR-/HER2+ subtype and 92.2% in the HR+/HER2+ subtype versus 67.9% in patients with the HR-/HER2- tumour subtype.
The authors concluded that significant differences were observed in tumour characteristics between different subtypes of male breast cancers. The strongest example was seen in patients with triple-negative breast cancers, where diagnosis was likely to be made at a younger age and also demonstrated poorer one year survival.
They remarked that further research is needed into male breast cancer to better characterise the role of receptor subtypes in tumour pathology and outcome.