THE DESCRIPTIVE EPIDEMIOLOGY OF MALIGNANT CYSTOSARCOMA-PHYLLODES TUMORS OF THE BREAST

Background, Malignant cystosarcoma phyllodes tumors of the breast are rare fibroepithelial tumors. The epidemiologic features of these malignancies in a defined population have not previously been described. Methods. Incidence data were collected from 1972-1989 by the Cancer Surveillance Program, the population-based cancer registry for Los Angeles County. Results. The average annual age-adjusted incidence rate of malignant cystosarcoma phyllodes is 2.1 per 1 million women. Latina whites have a higher risk of this cancer than other racial-ethnic groups. The age-incidence curve shows that risk of cystosarcoma phyllodes peaks in the 45-49-year-old age group, but the age patterns vary by race-ethnicity, with Asian and Latina patients significantly younger, on average, than non-Latina white patients. The incidence rates of malignant cystosarcoma phyllodes were substantially higher in the 1980s than in the 1970s, particularly among Latina whites and Asians. For Latina whites, birthplace is a significant predictor of risk. Women born in Mexico and Central and South America are at threefold to fourfold greater risk of malignant cystosarcoma phyllodes tumors than Latina whites born in the United States. Conclusions. The epidemiology of malignant cystosarcoma phyllodes tumors of the breast is strikingly different from that of the more common histologic types of breast cancer. The high risk in Latina immigrants may offer an important clue as to the cause of this rare tumor.