[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.