Expression of secreted protein acidic and rich in cysteine (SPARC) in breast cancer and response to neoadjuvant chemotherapy

Background: Secreted protein acidic and rich in cysteine (SPARC) has been suggested as a new biomarker and therapeutic target in breast cancer, as well as other tumor types. Patients and methods: We evaluated the frequency of SPARC expression among different molecular breast cancer subtypes and its role for therapy response after neoadjuvant chemotherapy. In this study, pretherapeutic core biopsies of 667 patients from the neoadjuvant GeparTrio trial were evaluated for SPARC expression by immunohistochemistry using a standardized immunoreactive score (IRS). Results: An increased SPARC expression (IRS ≥6) was observed in 26% of all tumors. In triple-negative tumors, SPARC expression was increased in 37% of tumors, compared with other molecular subtypes (23% HR+/HER2-, 29% HR+/HER2+ and 22% HR-/HER2+; P = 0.038). Increased SPARC expression was associated with an increased pathological complete response (pCR) rate of 27%, compared with 15% in tumors with low SPARC expression (P < 0.001). In the triple-negative subgroup, pCR rates were 47% in tumors with high SPARC expression, compared with 26% in tumors with low SPARC expression (P = 0.032). In multivariable analysis, SPARC was independently predictive in the overall population (P = 0.010) as well as the triple-negative subgroup (P = 0.036). Conclusions: SPARC is frequently expressed in breast cancer with triple-negative breast cancer revealing the highest expression rate. High SPARC expression of the primary tumor is associated with a higher chance of achieving a pathological complete remission after TAC or TAC-NX chemotherapy. As SPARC is an albumin-binding protein and might mediate intratumoral accumulation of albumin bound drugs, SPARC should be further evaluated as a predictive marker especially for response to albumin-bound drugs like nab-paclitaxel.