Clinical and molecular characterization of HER2-low metastatic colorectal cancer.

Abstract

e15573 Background: HER2 is a well-established biomarker and target in multiple tumor types, including metastatic colorectal cancer (mCRC). Despite the lack of HER2 amplification, certain HER2-low tumors were recently found to respond to novel HER2-directed antibody-drug conjugates, warranting an exploration of the clinical and molecular features of these entities. Yet, the real-world prevalence and the clinicopathologic characteristics of HER2-low mCRC are largely unknown. Here, we aim to describe the features of HER2-low mCRC and compare them to HER2-0 colorectal tumors. Methods: We retrospectively reviewed clinicopathologic data from consecutive patients with mCRC undergoing HER2 testing (immunohistochemistry [IHC] and in-situ hybridization [ISH], when appropriate) between 2017 and 2021 at Hadassah Medical Center, Israel. Tumors were defined HER2-positive (HER2+) if scored IHC 3 + or IHC 2+/ISH positive; HER2-low if scored IHC 2+/ISH negative or IHC 1+; HER2-0 if scored IHC 0. Genomic alterations were determined through a targeted next-generation sequencing (NGS) panel. Clinicopathologic and genomic data were compared between the cohorts with the Mann-Whitney or Fisher's exact test, and survival using Log-rank test. Results: A total of 100 consecutive mCRC patients were found eligible for our study, including 4 (4%) with HER2+, 30 (30%) with HER2-low, and 66 (66%) with HER2-0 disease. In the HER2-low group, five tumors were HER2 +2 / ISH negative, and 25 were scored HER2 +1. The fraction of female patients was 40% in HER2-low group, and 42% in the HER2-0 cohort (p > 0.99). The prevalence of mismatch repair deficient (MMR-D) tumors was also similar, with one MMR-D tumor in the HER2-low group, compared to 3 tumors in the HER2-0 (p > 0.99). 60% of the primary tumors in both groups originated in the left colon and rectum. Also, the prevalence of mucinous histology was comparable between the HER2-low and the HER2-neg cohorts (7.4% vs. 4.8%, p = 0.64). Among patients receiving local somatic NGS testing (n = 61), the fractions of patients with KRAS, BRAF, and TP53 mutations were largely comparable between the cohorts (Table 1). With a median follow up of 37 months, the median overall survival was 41 months for the HER2-low group and 51 months for the HER2-neg group (p = 0.15). Conclusions: In our cohort of patients with HER2-negative mCRC, the clinicopathologic and genomic characteristics of HER2-low and HER2-0 tumors did not differ significantly. However, our data suggest that HER2-low tumors represent a significant portion of mCRC, supporting further development of novel HER2-directed therapies for this population. Additionally, our data also support the notion that HER2-low, as currently defined, is not a distinct molecular subtype of mCRC. [Table: see text]