[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.

Metastatic Invasive Lobular Carcinoma of the Breast Presenting Peritoneal Metastasis with Bilateral Ureteral Obstruction.

The most common sites for recurrence of breast cancer are the lungs, liver, and bones. The frequency of peritoneal, gastrointestinal metastasis is significantly lower than those, and bilateral ureteral obstruction caused by peritoneal metastasis is relatively rare. A 66-year-old woman was referred to our hospital because of appetite loss and frequent urination. She was on adjuvant hormonal therapy for local recurrence of right breast cancer. She was diagnosed with bilateral ureteral obstruction due to extramural compression. Exploratory laparoscopy revealed omental cake and peritoneal nodules of which pathological examination showed peritoneal metastasis of invasive lobular carcinoma. Peritoneal metastases from breast cancer are unusual and consequently difficult to identify without non-invasive tools. Exploratory laparoscopy revealed that the cause of hydronephrosis in this case was peritoneal metastasis of invasive lobular carcinoma. Clinical history and histological study play a pivotal role in determining the correct diagnosis.