Peritoneal metastases from extra-abdominal cancer - A population-based study.

INTRODUCTION: Peritoneal metastases (PM) are predominantly seen as a manifestation of intra-abdominal malignancy such as colorectal or ovarian cancer. However, extra-abdominal primary cancer can also metastasise to the peritoneum. Population-based data on the incidence of PM from extra-abdominal cancer is lacking. This study aims to assess the patterns and survival of patients in Ireland with PM from extra-abdominal cancers. METHODS: The National Cancer Registry of Ireland database was interrogated to identify patients diagnosed with PM from extra-abdominal malignancy during the period 1994-2012. Patient demographics and tumour characteristics were analysed. RESULTS: 5791 patients were diagnosed with PM during the study period. Of these, 543 (9%) had an extra-abdominal primary malignancy. Breast (40.8%), lung (25.6%) and melanoma (9.3%) were the most common extra-abdominal cancers to develop PM. The majority of patients with peritoneal metastases of breast origin (75%) were diagnosed at a long interval (median interval 59.5 months; range = 1-485) from the diagnosis of the primary. The median survival from diagnosis of PM was 5.8 months compared with 22.6 months from diagnosis of stage IV disease without peritoneal involvement. Survival in patients with lung cancer and melanoma who developed PM was very poor and similar to that in patients with stage IV disease not involving the peritoneum. CONCLUSION: This is the first population-based study to report the incidence of PM secondary to extra-abdominal malignancy. The most common primary cancers were melanoma, breast and lung cancer. Metastatic disease to the peritoneum was uniformly associated with a poor prognosis.