Morphologic subtypes of lobular carcinoma in situ diagnosed on core needle biopsy: clinicopathologic features and findings at follow-up excision.

Lobular carcinoma in situ (LCIS) is currently classified as classic (CLCIS), florid (FLCIS), and pleomorphic (PLCIS). Given the rarity of FLCIS and PLCIS, information on their clinico-pathologic features and biologic potential remains limited. We evaluated the upgrade rates at excision of FLCIS and PLCIS diagnosed on inhouse core needle biopsy (CNB) and their clinical presentation and follow-up. Over a period of 11 and a half years, there were a total of 36 inhouse CNBs with pure PLCIS (n = 8), FLCIS (n = 24), or LCIS with pleomorphic features (LCIS-PF) (n = 4). The upgrade rates to invasive carcinoma or ductal carcinoma in situ (DCIS) were 25% for PLCIS (2/8), 17% for FLCIS (4/24), and 0% for LCIS-PF (0/4). The overall upgrade rate of PLCIS and FLCIS combined was 19% (6/32). All but one case (not upgraded at excision) were radiologic-pathologic concordant. Apocrine features, previously reported only in PLCIS, were also noted in FLCIS. HER2 overexpression was seen in 13% of cases. This study highlights the more aggressive biologic features of PLCIS and FLCIS compared to CLCIS and supports surgical management for these lesions.