MPNST

Sane, K.M., et al. (2010). A novel geranylgeranyl transferase inhibitor in combination with lovastatin inhibits proliferation and induces autophagy in STS-26T MPNST ce Ws. J Pharm Exp Ther 333 23-33. 

KER, keratin, detected by a mixture of GAMS.2, MAK-6, and AEl /AE3 EMA, epithelial membrane antigen VIM, vimentin DES, desmin MSA, muscle-specific actin SMA, smooth muscle (alpha isoform) actin GALD, h-caldesmon S-IOOP, S-100 protein OCN, osteocalcin LM, laminin UL, Ulex europaeus I lectin binding FS, fibrosarcoma SGRMS, spindle cell rhabdomyosarcoma LMS, leiomyosarcoma MPNST, malignant peripheral nerve sheath tumor MSS, monophasic spindle cell synovial sarcoma SCAS, spindle cell angiosarcoma KS, Kaposi s sarcoma FOS, fibroblastic osteosarcoma. 

TEE1 expression is prominent in synovial sarcoma, but not mimics such as MPNST and SFT. 

Leiomyosarcomas are most commonly found in the retroperitoneum in adults. They uncommonly occur in the deep soft tissues of the extremities but may be seen in more superficial sites, particularly in the dermis and subcutis. The differential diagnosis of LMS traditionally includes other sarcomas composed of intersecting spindle-cell fascicles, including fibrosarcoma, MPNST, synovial sarcoma, and spindle cell rhabdomyosarcoma. Additional conditions such as IMT (inflammatory pseudotumor), neurofibroma, and hemangiopericytoma (see Fig. 4.5) are also considerations. 

FIGURE 4.17 CD57 in malignant peripheral nerve sheath tumor (MPNST). Reactivity for S-100 protein, CD57, myelin basic protein, or collagen type IV is observed in greater than 85% of MPNSTs. 

Determinants associated with non-neoplastic Schwann cells and benign peripheral nerve sheath tumors are frequently detected in MPNSTs. They show reactivity for... 

Another spindle cell tumor that shares immunophe-notypic features with MPNST is monophasic synovial sarcoma (MSS). Roughly 40% of cases of MSS show SlOO staining, and approximately 30% are CD57-positive. " Cytokeratin subset analysis may be useful in difficult cases, because most synovial sarcomas are reactive for CK7 or CK19, or both. " In contrast, MPNSTs typically lack those proteins. CD 10-reactivity also favors a diagnosis of MPNST, whereas TLEl-positivity typifies MSS. 

Reports of MPNSTs with angiosarcoma-like images have also been described. Immunohistochemical analysis has confirmed the presence of endothelial differentiation in those cases. 

MPNSTs are negative for CK7 (which is positive in synovial sarcoma). 

The potential presence of CD34 in diverse polygonal-cell soft tissue tumors, including epithelioid LMS, epithelioid MPNST, clear cell sarcoma, and epithelioid sarcoma, has diminished its potential utility as an indicator of endothelial differentiation." " We also have observed that epithelioid angiosarcomas may be reactive... 

FIGURE 4.26 Epithelioid MPNST lacks distinguishing histologic features and requires intensive adjunctive study for proper diagnosis. 

Epithelioid MPNST is an extremely rare tumor variant that also has a histologic resemblance to melanoma, as well as metastatic carcinoma, CCS, and extrarenal rhabdoid tumor (Fig. 4.26). As a result, epithelioid MPNST is underrecognized as a diagnostic entity. 

Eabeling for S-100 protein is more frequently seen in epithelioid MPNSTs than in other forms of that tumor—at least 70% of cases, often with a strong and diffuse staining pattern. The majority of these tumors... 

Soft tissue sarcomas with a potentially pleomorphic histologic appearance (Fig. 4.28 see Table 4.7) include so-called MFH (undifferentiated pleomorphic sarcoma), pleomorphic rhabdomyosarcoma, pleomorphic or dedifferentiated liposarcoma, dedifferentiated LMS, and pleomorphic MPNST. 

Malignant peripheral nerve sheath tumor (MPNST) may likewise assume a pleomorphic appearance. In most instances, that tumor variant shows patterns of reactivity for S-100 protein, CD56, CD57, and collagen type IV that are superimposable with those of better differentiated (spindle cell) MPNSTs." In the absence of focal S-100 protein expression and foci with conventional appearances, it is very difficult (if not impossible) to render this diagnosis with certainty. Unlike spindle cell variants of MPNST, pleomorphic subtypes have not been shown to be desmin-reactive. 

Round cell liposarcoma is a morphologic variant of high grade MLPS that may resemble extraskeletal chondrosarcoma, cellular peripheral nerve sheath tumors, or even metastatic poorly differentiated carcinomas. S-100 protein and vimentin are seen in all these tumor types. MPNSTs that are similar microscopically to round cell liposarcoma may express CD56 or myelin basic protein, unlike adipocytic lesions. 

Hirose T, Scheithauer BW, Sano T. Perineurial malignant peripheral nerve sheath tumor (MPNST) A clinicopathologic, immunohistochemical, and ultrastructural study of seven cases. Am J Surg Pathol. 1998 22 1368-1378. 

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