Are Encapsulated Papillary Carcinomas of the Breast In Situ or Invasive? A Basement Membrane Study of 27 Cases

Encapsulated papillary carcinoma (EPC) of the breast is traditionally considered a variant of ductal carcinoma in situ (DCIS). However, recent studies show EPCs lack myoepithelial cells at their periphery, leading some to conclude that EPCs are invasive. We used a robust collagen type IV immunohistochemical procedure to assess invasion in 21 cases of pure EPC and 6 EPCs with adjacent invasive ductal carcinoma (IDC) and compared these results with those for papilloma, DCIS, and IDC. Moderate to intense collagen type IV expression was seen in all EPCs and was absent or decreased in all IDCs. All patients with pure EPC had negative axillary nodes with the exception of 1 who had a micrometastasis, and all were alive with no evidence of disease at follow-up (mean, 40.4 months). EPCs are in situ carcinomas with an excellent prognosis and can be managed with local therapy with or without sentinel lymph node biopsy.