Soft tissue sarcomas (STS) are a heterogeneous group of relatively uncommon tumors that show a broad range of differentiation, such as smooth muscle (leiomyosarcoma), adipocytic (liposarcoma), striated muscle (rhabdomyosarcoma), endothelial (angiosarcoma), or fibroblastic (e.g., dermatofibrosarcoma); they may arise in soft tissue or specific organs. Routinely-tabulated STS rates do not include the organ-specific sarcomas and thus underestimate true STS rates. We analyzed all1978-2001 SEER Program STS cases, including the organ-specific, according to demographic characteristics by histologic type and anatomic site to reveal clues for further research aimed at elucidating the etiology of these cancers. After excluding sarcomas of bones or joints and Kaposi’s sarcoma, 26,758 cases were available for analysis. Leiomyosarcomas accounted for 24% of the total, malignant fibrous histiocytomas 17%, liposarcomas 12%, dermatofibrosarcomas 11%, rhabdomyosarcomas 5%, angiosarcomas and malignant peripheral nerve sheath tumors each 4%, and other specified sarcoma types 8%; fibrosarcomas not otherwise specified (NOS) and sarcomas NOS accounted for 4% and 13%, respectively. Almost half the STSs arose in soft tissue (48%); the skin accounted for 14%, uterus 7%, retroperitoneum 7%, stomach 4%, and small intestine 3%; the remaining 17% arose in other sites. Total STS incidence rates were highest among black women (6.26/100,000 woman/years), followed by black men (5.99) and white men (5.49), with the lowest rate among white women (4.60). This pattern was largely driven by higher rates of leiomyosarcoma among blacks compared to whites, with rate ratios of 1.2 and 1.7 among males and females, respectively, especially those occurring in the uterus (1.7) and stomach (2.6 and 3.7) (the latter now classified as GIST). Dermatofibrosarcomas also were more frequent among blacks, with rate ratios of 1.6 among males and 1.8 females. Only angiosarcomas clearly occurred more frequently among whites than blacks. Total STS rates rose logarithmically with age following a modest early childhood peak due to rhabdomyosarcoma. Rates for both uterine leiomyosarcoma and dermatofibrosarcoma rose rapidly during the childbearing years before plateauing or even declining thereafter, with the peak for dermatofibrosarcoma about age 40 years and for leiomyosarcoma about age 50 years. From 1978-1983 to 1996-2001, age-adjusted rates for all STSs combined increased at 1.2% and 0.8% per year among white males and females, respectively, both statistically significant, while rates among blacks declined slightly. Incidence patterns varied considerably by histologic type, supporting that these tumors are etiologically distinct and that they should be considered separately in analytic studies.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]