A prospective study was carried out, between January 1980 and March 1982, of all women who presented to the Breast Cancer Unit, Guy's Hospital, with a second primary breast cancer. The percentage of new simultaneous tumours detected clinically or by mammography was approximately 3 per cent. Routine mammographic screening of the contralateral breasts of patients with unilateral disease increased the rate of detection, fivefold, of simultaneous bilateral cancers. The incidence of nonsimultaneous bilateral disease was 7.6 second cancers per thousand patients at risk per year. The annual rate of occurrence of second primary cancers was a constant event and showed no trend either to increase or to decrease with follow-up. However, the risk of a nonsimultaneous second cancer was strongly correlated with age at first primary. Women who developed their first breast cancers under the age of 40 years had three times the risk of developing a second breast cancer compared with those who developed their first cancer after the age of 40. The risk of a second nonsimultaneous primary was 5.9 times that of the risk of occurrence of cancer in the first breast in the general female population.

Thirty-five women with biopsy-proven Paget's disease of the nipple were treated over a 10 year period at the Breast Cancer Unit, Guy's Hospital. Twenty-four (69%) patients had Paget's disease without a palpable mass in the breast; eleven (31%) presented with a palpable mass and Paget's disease of the nipple. Definitive treatment consisted of modified radical mastectomy in 32 patients, radiotherapy only in 2, and one patient had no definitive treatment. All 11 patients with Paget's disease and an associated lump proved to have invasive ductal carcinoma; five also had associated positive axillary nodes. Nine of the 23 patients with nipple changes only, treated by mastectomy, also had invasive carcinoma; three of these had positive axillary nodes. The remaining 14 patients with nipple changes only were found to have in situ ductal carcinoma, which was extensive in the majority of cases. In 13 cases, histological sections of the nipple were examined by immunohistochemical staining which showed that the Paget's cells expressed a keratin phenotype that was specifically characteristic of simple epithelial cells as seen in glandular epithelium. This was quite unrelated to the normal keratin phenotype of the surrounding skin keratinocytes. Clinical, pathological, and immunohistochemical data suggest a mammary origin of the abnormal cells in Paget's disease of the nipple. Mastectomy appears to be the treatment of choice.

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