Ductal carcinoma in situ of the breast is malignant transformation of epithelial cells of the ductolobular system, without invasion through the basement membrane. Classically, ductal carcinoma in situ has presented as nipple discharge or a palpable mass. Until recently, the condition was regarded as an uncommon form of breast malignancy (representing about 1 percent of new breast malignancies) that was best treated by mastectomy. A review by Silverstein emphasizes that the incidence of ductal carcinoma in situ is increasing, and it is now known to be a heterogeneous group of conditions with a range of management options and prognoses.

Approximately 36,000 new cases of ductal carcinoma in situ are diagnosed each year in the United States, representing 17 percent of all breast cancers. Most cases are detected by mammography and occur in asymptomatic women. Several classifications are currently used according to histologic structure, nuclear grade, presence of necrosis and other factors. The experimental Van Nuys prognostic index is a scoring system based on recurrence data from a large series of patients that takes into consideration the nuclear grade and the presence of necrosis. Also, three predictors of recurrence (tumor size, margin width and pathologic classification) are given a score from one to three and then combined to estimate the prognosis as a numerical score from three (best) to nine (worst).

Classification and prognosis are particularly important in ductal carcinoma in situ because of the many controversies concerning management. In this series, the chance of invasive recurrence eight years after diagnosis was 7 percent, with a 1.4 percent risk of death from breast cancer. Only about 40 percent of low-grade lesions become invasive over a span of 25 to 30 years if left untreated. Approximately one half of all local recurrences become invasive.

Current treatments range from tumor excision to mastectomy. The width of the disease-free margin in the excised tissue is the most important factor in prognosis. Several studies have indicated that recurrence is minimal if margins of at least 10 mm are achieved. The role of radiotherapy following excision has become controversial. Although earlier studies clearly indicated an improved prognosis with postoperative radiotherapy, there is now considerable interest in subgroups of patients in whom the advantages of radiotherapy may be outweighed by side effects, cost and adverse factors. In particular, radiotherapy may change the texture of breast tissue, complicating mammographic detection of recurrence. Decisions about the extent of surgery and the use of radiotherapy must be made on an individual basis—but all patients with ductal carcinoma in situ of the breast must be clinically followed for life to ensure prompt recognition of any recurrence.