Genomic grade adds prognostic value in invasive lobular carcinoma.

BACKGROUND The prognostic value of histologic grade (HG) in invasive lobular carcinoma (ILC) remains uncertain, and most ILC tumors are graded as HG2. Genomic grade (GG) is a 97-gene signature that improves the prognostic value of HG. This study evaluates whether GG may overcome the limitations of HG in ILC. METHODS Gene expression data were generated from frozen tumor samples, and GG calculated according to the expression of 97 genes. The prognostic value of GG was assessed in a stratified Cox regression model for invasive disease-free survival (IDFS) and overall survival (OS). RESULTS A total of 166 patients were classified by GG. HG classified 33 (20%) tumors as HG1, 120 (73%) as HG2 and 12 (7%) as HG3. GG classified 106 (64%) tumors as GG low (GG1), 29 (17%) as GG high (GG3) and 31 (19%) as equivocal (cases not classified as GG1 or GG3). The median follow-up time was 6.5 years. In multivariate analyses, GG was associated with IDFS [HR(GG3 vs GG1) 5.6 (2.1-15.3); P < 0.001] and OS [HR(GG3 vs GG1) 7.2, 95% CI (1.6-32.2); P = 0.01]. CONCLUSIONS GG outperformed HG in ILC and added prognostic value to classic clinicopathologic variables, including nodal status.

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