In situ lobular carcinoma of the breast.

Nineteen patients who did not have mastectomy for in situ lobular carcinoma that was diagnosed by excisional biopsy were followed up for a period of seven to 21 years. In two patients, infiltrating carcinoma developed; each had mastectomies. They were followed up for 20 and 21 years. A third patient who previously had a mastectomy for infiltrating lobular carcinoma and who was being followed up for in situ lobular carcinoma in the contralateral breast died of metastatic disease. The remaining patients were found to be free of disease. These data support the concept that a small percentage (11%) of in situ lesions will progress to invasive tumors. Although mastectomy would seem to be the most prudent course, prolonged disease-free intervals were seen in patients who did not have mastectomy, suggesting close observation to be an alternative approach to this problem.