Basal phenotype: a powerful prognostic factor in small screen-detected invasive breast cancer with long-term follow-up

Objective To assess the frequency and prognostic significance of a basal phenotype in a group of women with screen-detected invasive breast cancers with long-term follow-up and to focus particularly on women with small (< 15 mm) breast cancers. Methods The study group was derived by finding women common to a consecutive series of 1944 invasive breast cancers diagnosed in Nottingham between 1986 and 1998 with a known basal phenotype status and a prospectively collected database of all screen-detected breast cancers. In total, 356 women constituted the study group. Pathological and radiological features were recorded. Basal cell markers used were CK5/6 (cloneD5/16134) and CK14 (clone LL002). Tumours were classified as of basal phenotype if > or = 10% staining was seen with either marker. Results Of all screen-detected lesions, 43 (12%) had a basal immunophenotype and 313 (88%) were non-basal. There were 15 (35%) and 40 (13%) breast cancer deaths in the basal group and non-basal groups, respectively (P=0.0006). On univariate analysis, nodal stage, histological grade, lympho-vascular invasion (LVI) status, invasive size and basal phenotype had prognostic significance. On multivariate analysis, basal phenotype, LVI and nodal stage maintain prognostic significance. Of the 189 women with < 15 mm lesions, eight of 20 (40%) of the basal group and eight of 169 (5%) of the non-basal group died of breast cancer (P<0.0001). On multivariate analysis, basal phenotype was the only factor to maintain independent prognostic significance. Conclusions Basal phenotype is a powerful prognostic factor for women with small screen-detected invasive breast cancer.