A study of the laterality of 980 patients with unilateral breast carcinoma revealed a leftiright ratio of 1.26. Detailed analysis disclosed a significant association between left predominance and the following clinico-pathologic features: menarche after age 13, age at diagnosis, parity especially among those between ages 40 and 54, and all histologic types except medullary tumors. When asynchronous bilateral carcinoma was documented, the disease first occurred more often in the left breast. Patients with simultaneous bilateral disease usually had a larger tumor on the left. Because differences in breast size were considered a contributing factor, relative breast volumes were computed from the mammograms of 174 healthy women; 55% were found to have a larger left breast. These data and other observations cited in the literature suggest that the asymmetry of breast carcinoma reflects differences in the sensitivity of the mam-mary glands to hormonal stimulation, resulting in unequal volumes of tissue at risk to develop carcinoma. Cancer 46:1705-1713, 1980. SMALL BUT CONSISTENT predominance of left-A sided breast cancer has been known for decades. Interest in the laterality of carcinoma in women was expressed almost 40 years ago by Fellenbergs who found a greater frequency of involvement of the left breast following a review of 986 cases identified by the Swiss Cancer Census for the years 1933-35. Although the left predominance has since been repeatedly noted, no satisfactory explanation has been found. The pur-The authors are indebted to the women who responded to the extensive interview during a very stressful period of hospitalization. Without their cooperation and the assistance of the members of the Breast Service, this prospective study would not have been possible. The authors also appreciate the help of Margaret McVicar, RN, with patient interviewing, Jean Foster and Catherine Clements for typing the manuscript, and the many volunteers who have assisted with computer data entry.

The authors review the records of 61 patients who had clinical mammographic examination and histologic lobular carcinoma in situ in at least one breast. An analysis was done to determine the tissue counterpart of positive mammographic findings as well as the accuracy and usefulness of mammography as an adjunct in the diagnosis of in situ lobular carcinoma.

A long-term prospective study of non-infiltrating breast carcinoma is being carried out in order to study the natural history and proper management of such lesions with particular interest in patients treated solely by local excision.During an 11-year period, 175 patients with lobular Ca in situ and intraductal Ca have been followed. None has developed recurrent disease including 18 undergoing wide local excision only. Histologic examination revealed that 36% of mastectomy specimens showed multifocal lesions, whereas only one of the patients treated by wide local excision had more than one microscopic focus. For these reasons total mastectomy is recommended as the treatment of noninfiltrating breast carcinoma. Subsequent development of contralateral cancer has occurred in ten patients.