[Re-Administration of Anti-EGFR Antibody Drugs for Unresectable Colorectal Cancer-Focusing on Tumor Markers].

The 2022 edition of the Guidelines for the Treatment of Colorectal Cancer described rechallenge therapy as a backward treatment for unresectable colorectal cancer, but currently, there is no evidence to support its benefit. We reviewed 6 cases of rechallenge therapy in which tumor marker trends could be followed in our department. Two cases had a rapid decline in tumor markers that was maintained for 7-8 months. In 3 cases, PR was also confirmed on imaging. In contrast, there was 1 case with no decrease in tumor markers at all. Our findings suggest that cases of wild-type RAS prior to rechallenge therapy and cases that are responsive to initial anti-EGFR antibody drugs may have been involved in the effect of rechallenge therapy.

[Two Cases of Synchronous Double Primary Prostate Cancer Accompanying Bone Metastasis and Colon Cancer].

We report two cases of synchronous double primary cancers, which were composed of prostate cancer accompanied by bone metastasis and colon cancer, within only five months of each other. The first was a 77-year-old man whose ECOG PS was 0. He was referred to our hospital in March 2020 because abdominal CT scan, which was performed at a clinic for the purpose of close examination of poor control of diabetes, showed wall thickening of the sigmoid colon. A further examination revealed prostate cancer accompanied by metastatic bone cancer and sigmoid colon cancer. Laparoscopic sigmoid colectomy was performed in April. Currently, six months after the surgery, both the prostate cancer and its accompanying metastatic bone cancer are well controlled by hormonal therapy. The second case was an 86-year-old man with an ECOG PS of 3 who was brought to our hospital by ambulance in August, 2020 because of fever and abdominal pain. A close examination revealed cecal cancer accompanying acute appendicitis. Prostate cancer accompanied by metastatic bone cancer was also diagnosed. Laparoscopic ileocecal resection was performed in the same month, but, unfortunately, the patient had repeated aspiration pneumonia and he finally passed away 43 days after surgery. We discuss the treatment strategy for colorectal cancer with synchronous or metachronous prostate cancer, which has been increasing in recent years, and include epidemiological considerations.