Background. Lobular carcinoma in situ (LCIS) is considered a risk factor-not a precursor-for both invasive lobular and ductal carcinoma. Florid LCIS (F-LCIS) is an architectural subtype of LCIS that does not express E-cadherin, yet has the histologic and often radiographic appearance of solid-type ductal carcinoma in situ (DCIS). Since DCIS is considered a precursor to invasive ductal carcinoma, should F-LCIS be considered a precursor to invasive lobular carcinoma (ILC)? Methods. Review of an institutional database identified cases of LCIS and solid-type DCIS diagnosed by excisional biopsy, segmentectomy, or mastectomy between 1991 and 2000 to determine the prevalence of associated invasive breast cancer. Archival specimens were evaluated for florid and nonflorid LCIS, nuclear grade of LCIS, and the presence and subtype of invasive breast cancer. Solid-type DCIS that lacked E-cadherin expression was classified as F-LCIS. Results. Of 210 consecutive specimens of LCIS examined, 171 had nonflorid LCIS (81%) and 39 had F-LCIS (19%). Nonflorid LCIS had a diffuse pattern, whereas F-LCIS appeared as discrete foci adjacent to ILC. An invasive component was identified with 87% of F-LCIS lesions versus 73% of nonflorid LCIS lesions (P = 0.064); this component was lobular in 100% of F-LCIS lesions versus 82% of nonflorid LCIS lesions, a significant difference (P = 0.0044) that persisted when the analysis was adjusted for nuclear grade (P = 0.0082). Conclusion. Its close spatial relationship to an invasive component and increased association with ILC suggest that F-LCIS may be a precursor for ILC.
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