Sarcomas and other malignancies of soft tissue, retroperitoneum, peritoneum, pleura, heart, mediastinum, and spleen

Background . Malignant neoplasms of the structural tissues, consisting mostly of soft tissue sarcomas, are morphologically diverse and rarely treated for epidemiologic purposes as individual entities. Our understanding to date of the pattern of occurrence of sarcomas is based largely on reports of limited individual clinic experience or case‐control studies, each driven by a single hypothesis, and there have been virtually no descriptions according to specific morphologic type. Methods . The accumulated coverage of the SEER populations offers an opportunity to correct this deficit. Each of the diagnoses has been reported and coded using a single set of rules and described in relation to the population at risk in terms of age, sex, race, calendar period, anatomic location, and outcome. In addition, each morphologic type has been compared with each of the others with respect to the pattern of occurrence and survival. Results . For most of the individual morphologic entities, the pattern of occurrence is specific and unlike other patterns. Differences according to anatomic site, age, sex, race, and period‐specific survival were found. Partly because of changes in diagnostic criteria over the years, differences in secular trend, other than that for Kaposi's sarcoma, could not be verified. Although some types of sarcoma may have important genetic determinants, there is evidence of environmental causation in others; for some varieties both genetic and environmental factors may operate. There is no evidence of improvements in survival. Conclusions . The most likely basis for the observed patterns are morphology‐specific differences in etiology and growth phase. Each of the entities should be considered etiologically distinct and should be studied individually whenever possible.