The 70-gene signature test as a prognostic and predictive biomarker in patients with invasive lobular breast cancer

Purpose: Genomic expression assays provide prognostic information and guide adjuvant chemotherapy decisions for patients with estrogen receptor (ER)-positive breast cancer. Few studies have evaluated the utility of such assays for invasive lobular carcinoma (ILC). The objective of this study is to evaluate the 70-gene signature test (ST) as a prognostic and predictive tool for ILC using a national cancer database.

Methods: We identified patients diagnosed with stage I-III ER-positive ILC from 2004 to 2016 using the National Cancer Database. All patients underwent 70-gene ST testing. We used the Kaplan-Meier method and Cox proportional hazard analyses to determine overall survival based on genomic risk classification. We also determined the benefit of adjuvant chemotherapy for patients with high-genomic risk ILC based on 70-gene ST testing.

Results: We identified 2610 patients with ILC who underwent 70-gene ST testing; 280 (11%) were classified as high genomic risk. Five-year overall survival rates were significantly worse for patients classified as high risk (83%) as compared with those classified as low risk (94%, p < 0.05). In Cox models, high genomic risk was independently associated with a significantly increased hazard of death. In our Cox models of patients who were high genomic risk, adjuvant chemotherapy was not significantly associated with improved overall survival.

Conclusion: In this large database study, we found that the genomic risk category determined by the 70-gene ST was significantly associated with survival outcomes for patients with ILC. However, the 70-gene ST failed to predict the benefit of adjuvant chemotherapy for patients with high genomic risk.