OBJECTIVETo study the expression of carbonic anhydrase (CA) IX and its significance in molecular subtyping of breast carcinomas. METHODL MaxVision immunohistochemical staining was used to examine the expression of ER, PR, HER2, CK5/6, EGFR, and CA IX in 117 cases of breast invasive ductal carcinomas.

RESULTSThe patients' age ranged from 25 to 71 years (mean 49.6 years). All the 117 cases were subclassified into five subtypes, with 66 (56.4%) luminal A, 6(5.1%) luminal B, 10 (8.6%) HER2 positive, 20 (17.1%) basal-like, and 15 (12.8%) unclassified tumors. The expression of CA IX in luminal A and basal-like breast cancers was 13.6% (9/66) and 8/20, respectively, with a significant difference (P < 0.05). Among the luminal A cancers, the expression of CA IX in tumors > 2 cm (7/27, 25.9%) was significantly (P < 0.05) higher than that of tumors ≤ 2 cm (2/39, 5.1%). The expression of CA IX in grade 3 invasive ductal carcinoma (18/50, 36.0%) was significantly higher than that in grade 1 (2/21, 9.5%) and 2 (7/46, 15.2%) tumors (both P = 0.006). In CA IX-negative of invasive ductal carcinoma, the expression of ER and PR was 61.1% (55/90) and 55.6% (50/90), respectively; whereas in CA IX-positive cancers, the expression of ER and PR was 37.0% (10/27) and 29.6% (8/27), respectively. The expression of hormone receptors in CA IX-negative tumors was significantly higher than that in CA IX-positive tumors (for both ER and PR, P < 0.05).

CONCLUSIONSThe expression of CA IX correlates not only with molecular subtypes of breast cancer, but also with the grading, hormone receptors and diameter of mammary invasive ductal carcinoma. CA IX is a relative independent marker of poor prognosis in breast cancer.