Infantile Myofibroma: Case Report and Review of the Literature.

We report a case of solitary infantile myofibroma (IM) with partially CD34-positive neoplastic cells on the back of a newborn boy. Ultrasonography showed a multilocular mass with a hypoechoic center surrounded by an isoechoic rim. Histopathological analysis revealed that the lesion was composed of small, round cells that were tightly packed and uniform. The cells had oval nuclei and were pale, CD34-positive, and richly cellular. They had interlacing fascicles of spindle cells with features of myofibroblasts with α-smooth muscle actin positivity. We speculate that neoplastic cells in most IMs differentiate towards myofibroblasts. However, in rare cases, their differentiation is more primitive and they express CD34, with or without α-smooth muscle actin expression.

The pericyte antigen RGS5 in perivascular soft tissue tumors.

Perivascular soft tissue tumors are relatively uncommon neoplasms of unclear lineage of differentiation, although most are presumed to originate from or differentiate to pericytes or a modified perivascular cell. Among these, glomus tumor, myopericytoma, and angioleiomyoma share a spectrum of histologic findings and a perivascular growth pattern. In contrast, solitary fibrous tumor was once hypothesized to have pericytic differentiation--although little bona fide evidence of pericytic differentiation exists. Likewise the perivascular epithelioid cell tumor (PEComa) family shares a perivascular growth pattern, but with distinctive dual myoid-melanocytic differentiation. RGS5, regulator of G-protein signaling 5, is a novel pericyte antigen with increasing use in animal models. Here, we describe the immunohistochemical expression patterns of RGS5 across perivascular soft tissue tumors, including glomus tumor (n = 6), malignant glomus tumor (n = 4), myopericytoma (n = 3), angioleiomyoma (n = 9), myofibroma (n = 4), solitary fibrous tumor (n = 10), and PEComa (n = 19). Immunohistochemical staining and semi-quantification was performed, and compared to αSMA (smooth muscle actin) expression. Results showed that glomus tumor (including malignant glomus tumor), myopericytoma, and angioleiomyoma shared a similar diffuse immunoreactivity for RGS5 and αSMA across all tumors examined. In contrast, myofibroma, solitary fibrous tumor and PEComa showed predominantly focal to absent RGS5 immunoreactivity. These findings further support a common pericytic lineage of differentiation in glomus tumors, myopericytoma and angioleiomyoma. The pericyte marker RGS5 may be of future clinical utility for the evaluation of pericytic differentiation in soft tissue tumors.

Inflammatory myofibroblastic tumour of the urinary bladder: the role of immunoglobulin G4 and the comparison of two immunohistochemical antibodies and fluorescence in-situ hybridization for the detection of anaplastic lymphoma kinase alterations.

AIMS: We examined gene rearrangement and the expression of anaplastic lymphoma kinase (ALK) in urinary bladder inflammatory myofibroblastic tumour (IMT) using fluorescence in-situ hybridization (FISH) and two immunohistochemical antibodies to ALK. We also investigated whether IMT represents an immunoglobulin (Ig)G4-related disease. METHODS AND RESULTS: The performance of the Dako FLEX ALK monoclonal antibody (CD246) and the Cell Signaling Technology ALK (D5F3) XP monoclonal antibody were compared. Overall, 11 of 16 tumours showed ALK expression by immunohistochemistry (69%). Ten demonstrated ALK expression with both stains and one was positive with D5F3 but not CD246 (91% correlation). The D5F3 antibody yielded a stronger staining intensity and a higher sensitivity. Nine tumours demonstrated ALK rearrangements (56%) by FISH. Three were ALK(+) by immunohistochemistry but negative for rearrangement by FISH, whereas one showed rearrangement by FISH but was negative by immunohistochemistry. In total, 12 tumours were positive for ALK abnormalities (75%). Using current criteria, no cases were classified as an IgG4-related disease. CONCLUSIONS: The ALK D5F3 immunohistochemical stain showed superior staining characteristics compared with ALK CD246. Discrepancies in the results between FISH and immunohistochemistry for ALK abnormalities may have causes that are multifactorial. By current criteria, IMT does not represent an IgG4-related disease.