Primary peritoneum carcinomatosis, what is this?

Primary starts there: The most common cause of peritoneal carcinomatosis is from ovary. It is not the glandular cells but the surface epithelium of the ovary that gives rise to this tumor which first spreads to omentum and then diffusely to bowel and peritoneum. If in the presence of carcinomatosis the ovaries are normal it is most common to find the site arising from epithelial cells of peritoneal origin.