Previous studies have suggested that breast cancer in young women has more aggressive biological features and poorer prognosis. However, the role of biological markers in these patients is not well understood. We aimed to learn more about this disease in a cohort of 125 young women from Singapore, Japan and Hong Kong, aged 35 years or less, with invasive breast cancer by evaluating the expression of vimentin and the basal cytokeratins CK14, CK5/6 and 34 beta E12. Both standard paraffin sections and tissue microarrays were used in the immunohistochemical evaluation of expression patterns of these four biological markers. CK5/6, CK14, vimentin and 34 beta E12, in increasing order of proportion, were detected in invasive carcinomas. Basal cytokeratins and vimentin showed significant inverse relationship with estrogen and progesterone receptor status while CK14 expression was found to be directly associated with c-erbB2 status. Basal cytokeratins and vimentin immunoreactivities were directly associated with CD117 and EGFR expression. Vimentin and 34 beta E12 immunopositivity correlated with tumor size, while vimentin was associated with higher histological grade. Our findings are in concert with reports that expression of basal cytokeratins and vimentin is correlated with adverse pathological parameters.