Clinicopathologic features of ductal carcinoma in situ in young women with an emphasis on molecular subtype.

Young women with ductal carcinoma in situ treated by breast-conserving therapy have a higher recurrence rate than do older women, and a younger age at diagnosis is associated with worse overall survival after recurrence. This study explores the clinical, pathologic, and immunohistochemical characteristics of ductal carcinoma in situ lesions diagnosed in women 40 years and younger with a focus on molecular subtypes to elucidate features that may contribute to the purported worse outcome for this patient population. Forty-one patients diagnosed with ductal carcinoma in situ at age 40 years and younger were identified over a 10-year period; 31 cases were used to construct tissue microarrays. The microarrays were labeled with antibodies to estrogen receptor, progesterone receptor, HER2, Ki-67, CK5/6, epidermal growth factor receptor, and p53 and subsequently classified as luminal A, luminal B, HER2, basal-like, or unclassifiable triple negative. All patients had high-grade (73.2%) or intermediate-grade (26.8%) ductal carcinoma in situ. The molecular subtype breakdown was 61.3% luminal A, 22.6% luminal B, 13% HER2, and 3.1% unclassifiable triple negative. The mean Ki-67 by subtype was 4.2%, 14%, 9.5%, and 50%, respectively. Mastectomy was performed in 33 patients (80%). Eight patients (20%) underwent excisional biopsy without subsequent mastectomy. In addition to a predominance of high-grade lesions, young patients had a high proportion of luminal B subtype, which may contribute to an increased rate of local recurrence in this population. A larger series is necessary to confirm the impact that the molecular subtypes of ductal carcinoma in situ in younger patients might have on outcome.