Sperm-associated antigen 5 (SPAG5) represents a novel oncogene in estrogen receptor (ER)–positive luminal-B breast cancer. The authors of this study evaluated the association of SPAG5 gene and protein expression and treatment response in 12,270 patients with ER-positive breast cancer. Overexpression was associated with higher odds of a pathologic complete response. Furthermore, among women with SPAG mRNA expression, the addition of adjuvant chemotherapy to adjuvant endocrine therapy was associated with superior 5-year distal relapse–free survival in patients both with and without nodal involvement compared with adjuvant endocrine therapy alone.
The authors conclude that SPAG5 transcript and SPAG5 protein expressions could help guide the treatment of ER-positive breast cancer, but further validation and prospective trials are needed.