Both IGHA2 and IGJ mRNA expression were positively associated with prognosis in the partially overlapping triple-negative (HR = 0.47, 95% CI: 0.27, 0.77 for IGHA2 and HR = 0.58, 95% CI: 0.39, 0.93 for IGJ) and basal-like (HR = 0.68, 95% CI: 0.52, 0.88 for IGHA2 and HR = 0.69, 95% CI: 0.51, 0.94 for IGJ) breast cancers, whereas neither IGHM nor IGHG1 mRNA was significantly associated with prognosis in these groups. Here, IGHM is linked to breast cancer.