[308] Lobular Carcinoma In Situ Variants Misinterpreted as Ductal Carcinoma In Situ in Core Biopsy: Incidence and Significance

ME Sullivan, SA Khan, B Susnik. Northwestern University, Feinberg School of Medicine, Chicago, IL

Background: Differentiating ductal (DCIS) vs. lobular carcinoma in situ (LCIS) on core biopsy (CB) has important clinical implications. Recently described LCIS variants, such as LCIS with necrosis (LCIS-N) and pleomorphic LCIS (LCIS-P), share some morphologic and biologic features with DCIS and can make this morphologic distinction more difficult. However, E-cadherin (EC) has been shown to be helpful in borderline cases. In this study, we performed EC immunostains on CB with a diagnosis (DX) of solid DCIS to determine the incidence of LCIS misdiagnosed as DCIS and reviewed the clinical information to determine the significance.
Design: Consecutive CB with an original DX of predominantly solid DCIS, with or without invasive carcinoma (IC), performed between 1/03 and 12/05 were included (N=139). Upon review cases with significant micropapillary or cribriform architecture or insufficient remaining tissue were dropped. EC was performed on the 82 remaining CB. On review, the DX of LCIS was based on EC negativity as well as morphology. LCIS-P DX required LCIS cells with cellular pleomorphism and nuclear size >3.5x a lymphocyte. In LCIS-N the CIS cells with classic lobular cytology displayed luminal necrosis. Subsequent surgical excision (SSE) was reviewed in selected cases.
Results: In 6 cases the tissue was insufficient for EC interpretation. Remaining cases (N=76) included 55 CIS without and 21 with associated IC. Upon review of HE and EC, 18/76 (24%) of all solid DCIS (with or without IC) was reclassified as LCIS including 9 variants (3 LCIS-P, 6 LCIS-N) and 9 classic LCIS (LCIS-C). In all the reclassified cases (with and without IC) the most common original DX was grade 1 solid DCIS. Overall, 35% (12/34) of grade 1, 18% (4/22) of grade 2 and 10% (2/20) of grade 3 solid DCIS was EC negative.

Cases Reclassified as LCIS

Original Diagnosis (w/o IC)	LCIS-N	LCIS-P	LCIS-C
Grade 1 (N=7)	0	0	1
Grade 2 (N=32)	5	1	0
Grade 3 (N=16)	0	0	0

In the group of DCIS without associated IC, the DX was changed to LCIS variant in 11% (6/55) cases. Two were upstaged to invasive lobular carcinoma in SSE. A single case of LCIS-C had unwarranted SSE (1/55, 2%).
Conclusions: In the three years included in the study, 13% of solid DCIS diagnosed in CB without IC had DX revised to LCIS. The majority of these were LCIS variants requiring complete excision like DCIS, therefore surgical management was unaffected. However, this distinction has treatment implications as radiation therapy is not indicated for any LCIS.
Category: Breast

Tuesday, March 10, 2009 9:30 AM

Poster Session III # 35, Tuesday Morning