Immunocytochemical staining of pS2 protein in fine-needle aspirate from breast cancer is an accurate guide to response to tamoxifen in patients aged over 70 years.

Fine-needle aspirates from 52 breast cancers in 50 patients over 70 years of age were immunocytochemically stained for pS2 protein. All patients were treated with tamoxifen 40 mg/day and followed up at intervals of 2 months. The size of the tumour was serially assessed with calipers and portable ultrasonography. Change in tumour size was confirmed mammographically. Clinical monitoring was performed bind of the pS2 status. Twenty-five tumours were pS2 positive, of which 23 showed a significant response; ten went into complete remission (mean time to complete remission 6.8 (range 2-14) months) and 13 demonstrated partial remission (mean follow-up 8.9 (range 6-19) months). Two tumours remained static. Twenty-seven tumours were pS2 negative and none of these responded to tamoxifen; six remained static (mean follow-up 11.5 (range 6-14) months) and 21 progressed (mean time to progression 7.0 (range 3-14) months) (P < 0.001). Immunocytochemical assessment of fine-needle aspirates from elderly women with breast cancer accurately predicts a worthwhile response to tamoxifen.