Descriptive study comparing outcomes of classic and nonclassic lobular carcinoma in situ (florid and pleomorphic) initially diagnosed on core needle biopsy.

The lobular carcinoma in situ (LCIS) subtypes include classic (CLCIS), pleomorphic (PLCIS), and florid LCIS (FLCIS). The CLCIS is considered a breast cancer risk factor, but clinical significance and natural history of other LCIS subtypes are unclear. The outcome data on PLCIS and FLCIS is limited. The aim of current study is to compare excision and follow-up findings of CLCIS and nonclassic LCIS (NCLCIS). The breast needle biopsies (NBs) with LCIS during 01/2007-12/2017 were identified. The imaging, clinical findings, and outcome were compared between CLCIS and NCLCIS. A total of 36 NBs from 32 patients with NCLCIS (14 PLCIS & 22 FLCIS) and 73 NBs from 68 patients with CLCIS were identified. The NCLCIS patients were older (57 vs 52 years; P = .02) and presented more often with calcifications (78% vs 44%; P = .01). Seven (19%) PLCIS were initially diagnosed as ductal carcinoma in situ (DCIS). The microscopic invasion was frequent with NCLCIS (25%). No invasion was identified in NBs with CLCIS. A separate concurrent NBs with a carcinoma (29% vs 6%; P = .018) or ductal atypia (12% vs 3%; P = .1) was more frequent with CLCIS. The upgrade rate (invasion or DCIS) was higher with NCLCIS (25% vs 4%). Four NCLCIS developed ipsilateral recurrences: 2 NCLCIS, 1 IDC, and 1 ILC (50; 10-96 months). No breast event was reported in 24 pure CLCIS (60; 8-144 months). Invasive carcinoma with NCLCIS, unlike CLCIS, is always lobular type. Recurrences following NCLCIS are ipsilateral lobular tumors. NCLCIS subtypes are nonobligate precursors to invasive lobular carcinoma.