[A Case of HER2-Positive Advanced Gastric Cancer with a Pathological Complete Response to Neoadjuvant Chemotherapy with S-1/CDDP/Trastuzumab].

A 61-year-old man was referred to our hospital because of epigastric pain. Upper gastrointestinal endoscopy revealed a type 2 tumor at the gastric antrum, which was diagnosed as gastric adenocarcinoma (tub1) by pathological examination and was HER2 positive 3+ by the IHC method. Abdominal computed tomography revealed multiple metastases to regional lymph nodes (LNs), including bulky nodes at No. 3, 6, and 11p stations. In particular, No. 6 LN was 43 mm in diameter and had invaded to the pancreas. The clinical stage was Ⅲc (T4aN3M0) and neoadjuvant chemotherapy was conducted using S-1/CDDP/trastuzumab. After 2 cycles of chemotherapy, a partial clinical response was obtained and distal gastrectomy with LN dissection (D2 plus No. 16 LN) was performed. The pathological specimens showed no residual cancer cells in the stomach and LNs (Grade 3: pCR). Adjuvant chemotherapy was not administered. The patient is alive 10 months after the surgery with no evidence of recurrence.