In lung cancer cyclooxygenase-2 (COX-2) expression has been reported to stabilise survivin, an inhibitor of apoptosis (IAP) which prevents cell death by blocking activated caspases. COX-2 expression limits the ubiquitination of survivin, protecting it from degradation. To determine if COX-2 expression in breast cancer showed an association with survivin expression, we assessed the levels of each protein in ductal carcinoma in situ (DCIS) and invasive breast cancer (IBC); relating expression patterns to recurrence of DCIS after surgery. Patterns of COX-2 and survivin expression were determined by intensity-graded immunohistochemistry of the primary tumours. Patients with DCIS (n=161) which had either recurred (n=47) or shown no evidence of recurrence (n=114) 5 years following primary surgery were studied. These were compared to 58 cases of IBC. Survivin was expressed in the cytoplasm of 59% of DCIS and 17% of IBC. High levels of both cytoplasmic survivin and COX-2 expression significantly correlated to DCIS recurrence. COX-2 expression was present in 72% of DCIS, and levels of expression positively correlated with cytoplasmic survivin expression in DCIS and invasive disease. The majority of DCIS that recurred expressed both proteins (69%) vs 39% nonrecurrent. Recurrence was not seen in DCIS lacking both proteins at 5 years (P=0.001). Expression of the IAP survivin is increased in DCIS and correlates closely with COX-2 expression. Increased expression of IAP, (leading to reduced apoptosis) may explain the effect of COX-2 in increasing recurrence of DCIS after surgical treatment.