High prevalence of retinoblastoma protein loss in triple-negative breast cancers and its association with a good prognosis in patients treated with adjuvant chemotherapy.

Background: Triple-negative breast cancer (TNBC) is an aggressive disease, nevertheless exhibiting a high response rate to chemotherapy. Since the retinoblastoma protein (pRb) loss confers a high sensitivity to chemotherapy regimens, we evaluated the prevalence of pRb loss in TNBCs and its relevance on the clinical outcome of patients treated with adjuvant chemotherapy.

Patients And Methods: pRb status was prospectively evaluated by immunocytochemistry in 518 consecutive patients with complete receptor information. The predictive value of pRb status in TNBCs was determined according to the adjuvant therapeutic treatments.

Results: Fifty-three tumors were identified as TNBCs. The prevalence of pRb loss was significantly higher in TNBCs than in the other cancer subtypes. All patients with TNBCs lacking pRb and treated with systemic chemotherapy (cyclophosphamide, methotrexate and 5-fluorouracil) were disease free at a medium follow-up time of 109 months, whereas the clinical outcome of those expressing pRb was significantly poorer (P = 0.008). Analysis of disease-free survival including the established anatomo-clinical prognostic parameters indicated pRb loss as the only significant predictive factor.

Conclusions: pRb loss is much more frequent in TNBCs than in the other breast cancer subtypes. Patients with TNBCs lacking pRb had a very favorable clinical outcome if treated with conventional adjuvant chemotherapy.