The specific role of human epidermal growth factor receptor-2 (HER2) status in rectal cancers remains unclear. This study therefore aimed to explore clinicopathologic and molecular characteristics, and prognostic value of HER2-positivity in residual mid- and/or low-rectal cancers after preoperative chemoradiotherapy (CRT). Surgical specimens from 145 patients with residual rectal cancer after preoperative CRT between January 2006 and January 2011 were used to evaluate HER2 status. HER2 protein expression and gene amplification were determined using immunohistochemistry (IHC) and silver in situ hybridization (SISH) on whole tissue sections, respectively. Polymerase chain reaction was used to analyze molecular characteristics, including microsatellite instability (MSI) and mutations in KRAS exon 2 (codon 12 and 13) and BRAF V600E mutation. Of 139 eligible patients, 8 (5.8%) had HER2 overexpression (IHC 2+ and 3+) that was not associated with clinicopathologic characteristics and patient survival, except positive circumferential resection margin (CRM) (P = 0.012). SISH was performed on 24 patient samples with IHC 1+ (n = 16), 2+ (n = 6), and 3+ (n = 2). HER2 amplification was identified in 3 patients (2.2%); however, this was also associated with positive CRM (P = 0.009) but not survival (all P > 0.05). Moreover, HER2 overexpression and amplification had no relationship with KRAS or BRAF mutations, and MSI status (all P > 0.05). HER2 positivity was found in a minority of rectal cancer patients and was not significantly associated with clinicopathologic and molecular characteristics. Our findings can be helpful in understanding the clinicopathologic bases of HER2 status in rectal cancers.
Keywords: Human epidermal growth factor receptor 2; Preoperative chemoradiotherapy; Prognosis; Rectal cancer; Silver in situ hybridization.