Regressive change in high-grade ductal carcinoma in situ of the breast: histopathologic spectrum and biologic importance.

High-grade ductal carcinoma in situ (HG-DCIS) of the breast often shows tumor attenuation and reactive fibrosis. These changes, previously described as "regressive," have been paradoxically associated with an increased risk of invasive carcinoma. We aimed to further characterize the spectrum of the so-called regressive changes (RCs) in HG-DCIS. We reviewed 52 consecutive cases of HG-DCIS on biopsy specimens followed by excision. RCs were divided into early (stage 1) and advanced (stages 2 and 3) stages according to the degree of ductal fibrosis and tumor effacement. The presence of inflammation, hormone receptor status, and diagnosis on excision were recorded. RCs were seen in 51 (98%) cases: 96%, 76.4%, and 39.2% cases showed stages 1, 2, and 3, respectively. Periductal T cells with a normal CD4/CD8 ratio were constantly seen. Advanced RCs and inflammation were more frequent in estrogen and progesterone receptor-negative tumors. RCs were not associated with invasion but correlated with a larger residual HG-DCIS volume on excision. Regression in HG-DCIS is frequent. It may reflect a targeted immune response to certain phenotypes, mainly hormone receptor-negative lesions. Nonetheless, RCs do not lead to complete tumor obliteration but correlate with aggressive tumor characteristics instead.