Background: Lobular neoplasia (LN) represents a spectrum of atypical proliferative lesions, including atypical lobular hyperplasia and lobular carcinoma-in-situ. The need for excision for LN found on core biopsy (CB) is controversial. We conducted a prospective multi-institutional trial (TBCRC 20) to determine the rate of upgrade to cancer after excision for pure LN on CB. Methods: Patients with a CB diagnosis of pure LN were prospectively identified and consented to excision. Cases with discordant imaging and those with additional lesions requiring excision were excluded. Upgrade rates to cancer were quantified on the basis of local and central pathology review. Confidence intervals and sample size were based on exact binomial calculations. Results: A total of 77 of 79 registered patients underwent excision (median age 51 years, range 27–82 years). Two cases (3 %; 95 % confidence interval 0.3–9) were upgraded to cancer (one tubular carcinoma, one ductal carcinoma-in-situ) at excision per local pathology. Central pathology review of 76 cases confirmed pure LN in the CB in all but two cases. In one case, the tubular carcinoma identified at excision was also found in the CB specimen, and in the other, LN was not identified, yielding an upgrade rate of one case (1 %; 95 % CI 0.01–7) by central pathology review. Conclusions: In this prospective study of 77 patients with pure LN on CB, the upgrade rate was 3 % by local pathology and 1 % by central pathology review, demonstrating that routine excision is not indicated for patients with pure LN on CB and concordant imaging findings.
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