A rare case of primary transverse colon adenocarcinoma penetrating the abdominal wall.

Colorectal cancer (CRC) is the third most prevalent malignancy globally and the second leading cause of cancer mortality as of 2020. Its clinical presentation varies by stage, progressing from asymptomatic early disease to advanced symptoms (e.g., rectal bleeding, bowel habit alterations), while unusual manifestations may signal locally advanced disease. Locally advanced CRC is rare, without metastasis representing a critical therapeutic window for curative surgery or neoadjuvant therapy. However, primary locally advanced CRC penetrating the abdominal wall from the intra-abdominal cavity remain unreported. In this report, we describe a rare case of a 78-year-old male who had primary invasive transverse colon adenocarcinoma penetrating the abdominal wall, forming an externally visible mass measuring approximately 9 × 5 cm without lymph node or distinct metastasis. After the pathologically diagnosis of colon adenocarcinoma, the patient received a radical resection surgery combined with abdominal wall reconstruction using a skin flap, followed by six months of capecitabine-based adjuvant chemotherapy. The patient showed no relapse or progression during the one year follow-up after the operation. This rare case highlights the ongoing challenges in managing locally advanced CRC and underscores the potential benefits of active curative treatment strategies for such patients.