Granular Cell Variant of Epithelioid Cell Histiocytoma

Epithelioid Fibrous Histiocytoma With Chondroblastoma-Like Features: A Report of a Rare Entity and Discussion of Related Diagnostic Challenges

ABSTRACT

Epithelioid fibrous histiocytoma (EFH) is an uncommon benign skin lesion. It is distinct from FH by virtue of its recurrent anaplastic lymphoma kinase (ALK) gene rearrangements and immunohistochemical expression of ALK protein. It often poses a challenge in interpretation. Clinically, it is characterized by a flesh-colored papule/nodule on an extremity of a young to middle-aged individual. Microscopically, it is represented by a circumscribed dermal papule/nodule composed of sheets of plump epithelioid cells, forming whorled aggregates around numerous intralesional vessels. Immunohistochemistry, notably ALK positivity and relevant negative stains, serves to distinguish EFH from its morphological mimics. Rare examples of chondroblastoma-like EFH and EFH with osseous metaplasia are recorded in the literature. Our case is of a 58-year-old man who attended an oculoplastic surgeon because of an exophytic cutaneous nodule on the right upper eyelid. The lesion was excised. Microscopically, it displayed morphological and immunohistochemical features of EFH. Of interest, discrete foci of chondro-osseous change, including chondroblastoma-like pericellular calcification, osteoid formation, and osteoclast-like giant cells, were noted throughout the lesion. A diagnosis of EFH with chondroblastoma-like features was made. Of interest, the changes observed in this EFH serve to link the previously reported examples of pure chondroblastoma-like EFH and EFH with osseous metaplasia. This morphological variant of EFH adds to the existing diagnostic challenge presented by these lesions, particularly in the distinction from other calcifying tumors of the skin.

Three additional cases of non-neural granular cell tumor with novel immunohistochemical findings

BACKGROUND

Non-neural granular cell tumor (NNGCT) is an uncommon neoplasm of controversial histogenesis and its histopathologic differential diagnosis includes, in addition to conventional GCT, other dermal tumors that may exhibit granular cell change.

METHODS

Three patients with a diagnosis of NNGCT were identified in the authors' files. Hematoxylin and eosin-stained sections and immunohistochemical studies were performed.

RESULTS

Histopathological study of the three lesions showed dermal proliferation of granular cells arranged in thick fascicles between collagen bundles. The lesions showed positivity for Factor XIIIa, CD163, CD68, NKIC3, vimentin, ALK, fascin, and cyclin D1.

CONCLUSION

To our knowledge, positivity for cyclin D1 has not been reported to date in NNGCT. In borderline cases, where the diagnosis is unclear despite histopathologic and immunohistochemical findings, positivity for cyclin D1 may favor the diagnosis of NNGCT. Further investigations to assess the differentiation of this rare neoplasm are needed.

Cutaneous Non-Neural Granular Cell Tumors Harbor Recurrent ALK Gene Fusions

Non-neural granular cell tumor (NNGCT; also known as primitive polypoid granular cell tumor) is a rare neoplasm composed of large ovoid cells with abundant granular cytoplasm, variable nuclear pleomorphism, and the potential for regional lymph node spread. In contrast to conventional granular cell tumor (GCT), NNGCT lacks S100 expression and can exhibit greater nuclear atypia and mitotic activity. Therefore, we investigated clinicopathologic features of 12 NNGCT, and also used next-generation sequencing to identify potential driver events in a subset of NNGCT and 6 GCT. NNGCT demonstrated mild-to-moderate nuclear pleomorphism, variable mitotic activity (0 to 10/10 high-power fields), and were S100. Genetic analysis of 5 cutaneous NNGCT revealed gene fusions involving the anaplastic lymphoma kinase gene (ALK) in 3 cases (60%). Specifically, an interstitial deletion of chromosome 2 resulting in an in-frame fusion of dyanactin 1 (DCTN1) to ALK was identified in 2 cases, and a translocation resulting in a fusion between sequestosome 1 (SQSTM1) on chromosome 5 and ALK was identified in one case. Two of 6 GCT (33%) showed gains of chromosome 7. No other molecular or chromosomal alterations were detected in NNGCT and GCT. ALK immunohistochemistry revealed weak-to-moderate positivity in 4/9 cutaneous NNCGT (44%) including all 3 tumors with ALK fusions. Three oral NNGCT lacked ALK expression. NNGCT with ALK immunostaining did not have morphologic features distinguishing them from those without ALK staining. Our results demonstrate that a subset of NNGCT harbor ALK fusions, suggest that NNGCT are molecularly diverse, and further substantiate NNGCT as distinct from GCT.

Granular cell differentiation: A review of the published work

Since the initial description of the granular cell tumor in 1926, numerous other neoplasms, both benign and malignant, have been described to exhibit granular cell change. In most cases, diagnosis remains straightforward via recognition of retained histopathological morphology of the archetypal tumor, despite the presence of focal granular appearance. However, tumors with granular cell differentiation can present a diagnostic challenge either by mimicking alternative diagnoses, or by failing to exhibit architectural clues of the primary entity, thus requiring an immunohistochemical work-up. In light of this, it is important to be aware of the various entities that have been reported to exhibit granular cell morphology. In this review such tumors are discussed along with pertinent clinical and histopathological features.

S-100 Negative Granular Cell Tumor of the Oral Cavity

Classic granular cell tumor is a mesenchymal neoplasm that commonly occurs on the skin, but is not infrequently found in the oral cavity, primarily on the dorsal tongue. Diagnosis is usually straightforward with hematoxylin and eosin stained slides. Immunohistochemical studies on classic granular cell tumor shows positive immunostaining for S-100 and vimentin, while CD68 is variably positive. We report a case of otherwise unremarkable oral granular cell tumor that was immunohistochemically negative for S-100, and positive for vimentin and CD68, and discuss the differential diagnosis. The results of the immunohistochemical studies in our case are compared with those of classic S-100 positive oral granular cell tumors, as well as cutaneous and oral S-100 negative granular cell tumors. Classic S-100 positive granular cell tumors and S-100 negative granular cell tumors of the oral cavity can only be distinguished by immunohistochemical studies; however, the necessity of this distinction is unclear, as both are benign lesions in which recurrence is unlikely.