Biological and clinical features of triple negative Invasive Lobular Carcinomas of the breast. Clinical outcome and actionable molecular alterations

Background: We report here for the first time, a comprehensive characterization of biological and clinical features of early-stage triple negative Invasive Lobular Carcinomas(TN-ILCs) Methods: We analyzed all consecutive patients with early-stage TN-ILC operated at two reference cancer-centers between 1994 and 2012. Primary objective was to assess the invasive disease-free survival(iDFS). Co-primary objective was to assess biological features of TN-ILCs, including molecular intrinsic subtypes based on PAM-50 assay, expression of androgen receptor (AR) and mutational status of ERBB2-gene. Additionally, DNA mutational status of an independent cohort of 45 TN-ILCs from three databases were analyzed, to confirm mutations in ERBB2-gene and to identify other recurrently mutated genes. Results: Among 4152 ILCs, 74(1.8%) were TN and were analyzed. The iDFS at 5 and 10 years of FUP were 50.4%(95%CI,38.0–61.6) and 37.2%(95%CI,25.5–48.8), respectively. The molecular subtype was defined through PAM50-classifier for 31 out of 74 TN-ILCs: 48% were Luminal-A(15/31), 3% luminal-B(1/31), 32% HER2-enriched (10/31), and only 16% basal-like(5/31). Luminal tumors expressed AR more frequently than non-luminal tumors (AR≥1% in 94% of luminal tumors versus 53% in non-luminal tumors; p-value = 0.001). 20% of TN-ILCs analyzed(7/35), harbored a pathogenetic and actionable mutation in the ERBB2-gene. Analysis of the independent cohort of 45 TN-ILCs from three different databases, confirmed similar percentage of pathogenetic and actionable mutations in ERBB2-gene(20%; 9/45). Among the top 10 molecular pathways significantly enriched for recurrently mutated genes in TN-ILCs(FDR<0.05), there were ErbB-signaling and DNA-damage-response pathways. Conclusions: TN-ILCs are rare tumors with poor prognosis. Their specific biological features require newly defined targeted therapeutic strategies