The pyrosequencing assay designed to detect E332K mutations in HER3 furin-like cysteine rich domain has also allowed us to detect a novel E332E synonymous mutation, which changes a GAG codon to a GAA codon (Figure 1).The E332E synonymous mutation was detected in a retroperitoneal leiomyosarcoma specimen (soft tissue sarcoma). The gene discussed is ERBB3; the disease is leiomyosarcoma.