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Myofibrosarcoma is a controversial neoplasm composed of cells with differentiation toward myofibroblasts. The authors report an unusual case of myofibrosarcoma in which, in addition to the characteristic features reported, tumor cells contained intracytoplasmic hyaline (fibroma-like) inclusion bodies. A 66-year-old man complained of a painless enlarged mass in his right shoulder over the previous 6 months. The tumor recurred 2 years after operation. On histologic examination, the tumor displayed diffusely infiltrative growth with isolation of individual skeletal muscle fibers. The tumor cells were most often arranged in an intersecting (herringbone) fascicular pattern but a vaguely storiform pattern was also observed. Cellularity varied from one area to another. The cells were spindle-shaped, with ill-define pale eosinophilic cytoplasm, and a wavy or tapering nucleus with fine chromatin and small nucleoli. Intracytoplasmic hyaline inclusion bodies of variable size, often located adjacent to the nucleus, were visible in numerous spindle and stellate cells. The mitotic index was 3/10 HPF. The tumor was scored as grade 1. Immunohistochemistry revealed positive staining to muscle-specific actin, desmin and vimentin in most tumor cells. Intracytoplasmic hyaline inclusion bodies did not react specifically to any one antibody, but showed a marked ring-like immune reaction, particularly to muscle-specific actin. Electron microscopy showed tumor cells with indented nuclei and small nucleoli, abundant rough endoplasmic reticulum, micropinocytotic vesicles, and longitudinally arranged fine filaments with focal electron-dense patches and subplasmalemmal plaques. The most striking feature was the presence of large, globular or ball-like, non-membrane-bound, randomly scattered clusters of fine filament, usually adjacent to the nucleus.

DIPNECH is characterized by neuroendocrine cell hyperplasia, tumorlets, and eventually carcinoid tumors. Although it is regarded by some authors as a preneoplastic condition, this issue is controversial. New pathologic criteria have recently been proposed for the diagnosis of DIPNECH, and a subgroup of carcinoid tumors expressing developing neural transcription factors (DNTFs), with clinicopathologic features similar to those of DIPNECH, has been recognized. This paper reports on the clinical and pathological findings in three cases of DIPNECH and investigates the expression of three DNTFs (TTF1, ASCL1, and POU3F2). All patients were female, with a mean age of 63 years, and all lesions were located in the periphery of the lung. In two cases, typical carcinoids were associated with a spindle-cell component. All neuroendocrine proliferations were DNTF positive. The morphologic (spindle-cell component), phenotypic (DNTF expression), and clinicopathologic (peripheral tumors, female predominance) similarities suggest that DIPNECH may be a preneoplastic lesion for peripheral carcinoids.