Differentiating ductal carcinoma in situ (DCIS) from lobular carcinoma in situ (LCIS) on core biopsy has important clinical implications. Lobular carcinoma in situ variants, including LCIS with necrosis and pleomorphic LCIS, share morphologic features with solid DCIS that may lead to misclassification.
(1) To review all LCIS variants diagnosed in core biopsies at Northwestern University, Feinberg School of Medicine, and determine the frequency of misinterpretation of variant LCIS as solid DCIS in archival core biopsies, and (2) to determine the frequency of upgrade to invasive carcinoma or DCIS in the surgical excision.
Consecutive core biopsies with original diagnoses of predominantly solid DCIS without invasion that were performed between January 2001 and December 2005 at Northwestern University, Feinberg School of Medicine, were selected for E-cadherin staining. The revised diagnosis of LCIS was based on E-cadherin negativity and morphology. The frequency of LCIS variants upgraded was then estimated from all core biopsies with original or revised diagnoses of pleomorphic LCIS or LCIS with necrosis.
Among 75 cases of solid DCIS, 10 (13.3%) were reclassified as LCIS, including 9 variants (5 pleomorphic LCIS, 4 LCIS with necrosis) and 1 classic LCIS. Twenty-eight patients comprised the entire group of LCIS variant cases (both reclassified and originally diagnosed cases). Seven patients with LCIS variants (25%) were upgraded to invasive lobular carcinoma in surgical excision (4 of 11 cases of LCIS with necrosis [36%] versus 3 of 17 cases of pleomorphic LCIS [18%]).
About one-tenth of solid DCIS diagnosed in core biopsies in the past may represent LCIS variants. These show a 25% upgrade to invasive lobular carcinoma in surgical excision. The distinction of an LCIS variant from DCIS is important because of its implications for radiation therapy, although it may not affect surgical management.