Inflammatory Leiomyosarcoma

The American Joint Committee on Cancer (AJCC) or Union for International Cancer Control (UICC) TNM system is appropriate.

The pathogenesis is not fully understood, but these tumors have a distinctive near-haploid genotype, with or without subsequent whole-genome doubling, and they are associated with striking myogenic gene expression. The near-haploidization is thought to be pathogenetically important. When analyzed by chromosome banding or genomic arrays, 10 of 11 inflammatory LMSs displayed near-haploidization, with or without subsequent whole-genome doubling(s). Although most chromosomes thus showed loss of heterozygosity, there was always retained heterozygosity for chromosomes 5 and 22, and often for chromosomes 18, 20, and 21. Apart from mutation of the NF1 gene in a subset of the cases, no additional somatic variants that could serve as driver mutations have been detected. Gene expression profiling has shown prominent differential expression of genes involved in muscle development and function.

Most tumors appear well circumscribed, with a maximum diameter of 3–12 cm. Cut surfaces are tan-yellow or red and soft/fleshy.

These tumors consist of eosinophilic spindle cells with blunt-ended elongated nuclei, arranged in fascicles or sometimes in a storiform fashion. The degree of nuclear atypia and pleomorphism varies, as does mitotic count, depending on histological grade. However, most cases appear to be low-grade. The striking and characteristic feature is the presence of a prominent, usually diffuse, inflammatory infiltrate, which often obscures the neoplastic cell population. The inflammatory component is usually dominated by small lymphocytes, sometimes admixed with plasma cells. Histiocytes are also often prominent and may have a xanthomatous appearance. In a minority of cases, the inflammatory infiltrate may consist mainly of neutrophils or eosinophils. Calcospherites (psammomatous calcifications) are a striking feature in some cases. Virtually all cases show immunopositivity for some combination of SMA, desmin, and caldesmon.

Not clinically relevant

Published follow-up data in inflammatory LMS are limited due to its rarity. Among 20 cases with follow-up, only 4 have been reported to metastasize, but duration of follow-up is < 5 years in most cases. Of the cases in which a near-haploid genotype has been well documented, the prognosis seems generally to be very good.

Not clinically relevant

Essential: fascicular proliferation of variably atypical eosinophilic spindle cells, which show mitotic activity; dense inflammatory infiltrate, most often lymphoid or histiocytic/xanthomatous, but the composition is variable; immunopositivity for smooth muscle antigens.