Cutaneous Clear Cell Neoplasms: A Histopathological Reappraisal

NONO::TFE3 fusion cutaneous epithelioid and spindle cell tumor: A case series

The NONO::TFE3 fusion has been described in MiT family translocation renal cell carcinomas as well as extracutaneous perivascular epithelioid cell tumors (PEComas). PEComas are known to express myogenic and melanocytic markers but SOX10 and p63 positivity has never been reported. We report two primary cutaneous tumors that morphologically and molecularly fit PEComas, both harboring the NONO::TFE3 fusion, but with an unusual immunophenotype of SOX10 and p63 positivity. One case was on an 80-year-old male's finger, and the other one was on a 72-year-old female's thigh. Both were well-circumscribed multinodular dermal tumors composed of nests of monotonous epithelioid to spindled cells with pale to vacuolated cytoplasm, some of which were arranged around blood vessels. Both tumors were positive for SOX10, S100, and p63, focally positive for Melan-A, and negative for myogenic markers. There are very little data regarding the molecular findings of primary cutaneous PEComas. While the NONO::TFE3 fusion has been identified in extracutaneous PEComas, it has never been reported in primary cutaneous cases. We believe these cases represent a previously undescribed subtype of cutaneous tumor which shows some immunophenotypic expression of melanocytic markers and we named these cases NONO::TFE3 fusion cutaneous epithelioid and spindle cell tumor. Further, we raise the question of whether this tumor should fall under the rubric of PEComa because of its morphology, partial expression of melanocytic markers, and the presence of the NONO::TFE3 fusion, or whether these tumors represent a separate novel class of tumors since the immunophenotypic expression of SOX10 and p63 is unusual for PEComas.

Metastatic melanoma and rare melanoma variants: a review

The histopathological diagnosis of melanoma is fraught with potential pitfalls. In the setting of cutaneous metastatic melanoma, it is important to recognise the various histological patterns that can be encountered from the more common to the rare, including epidermotropic, folliculotropic, naevoid, and blue naevus-like. In addition, melanoma is notorious for phenotypic plasticity. Thus, there are many different subtypes and cytomorphological variations that can be difficult to recognise as melanoma, particularly in the recurrent or metastatic setting. Select melanoma variants including primary dermal, clear cell, plasmacytoid, signet ring cell, small cell, myxoid, rhabdoid, and dedifferentiated melanoma will be discussed, in addition to composite melanocytic neoplasms. This review is intended to remind the practitioner of key concepts of metastatic disease and select rare melanoma variants, while providing practical guidelines for accurate diagnosis.

Clear Cell Proliferations of the Skin: A Histopathologic Review

ABSTRACT

Cutaneous clear cell proliferations encompass a heterogenous group of several primary cutaneous neoplasms and metastatic tumors with different histogenesis. Many of these clear cell proliferations may seem strikingly similar under the microscope resulting in challenging diagnosis. In many of these clear cell lesions, the reason for the clear or pale appearance of proliferating cells is unknown, whereas in other ones, this clear cell appearance is due to intracytoplasmic accumulation of glycogen, mucin, or lipid. Artifacts of tissue processing and degenerative phenomenon may also be responsible for the clear cell appearance of proliferating cells. Awareness of the histopathologic findings as well as histochemical and immunohistochemical techniques are crucial to the accurate diagnosis. This review details the histopathologic features of clear cell cutaneous proliferations, classifying them according their type of differentiation and paying special attention to the histopathologic differential diagnosis among them.

Clear cell sarcoma of soft tissue with eccrine differentiation: A case report and review of the literature

Clear cell sarcoma of soft tissue (CCSST) is a deep soft tissue tumor presenting in the extremities of young adults. Histopathologically, nests and sheets of polygonal cells with clear to eosinophilic cytoplasm separated by fibrous septa as well as occasional "wreath-like" giant cells are visualized. However, CCSST has been noted to have atypical histopathological features, such as epidermotropism or myxoid differentiation, or occurrence at unusual sites. Here, we present a case of eccrine ductal differentiation in CCSST. The patient, a 21-year-old woman, presented with a lump of 10-year duration sized 3 × 5 cm on the plantar surface of the fourth and fifth interdigital spaces. There had been an increase in size as well as pain and redness over 6 years. Besides the characteristic findings, there were ductal structures in continuity with the upper dermis indicative of ductal differentiation. The tumor stained positively for S100, HMB45, and succinic dehydrogenase; ducts stained positively for epithelial membrane antigen (EMA) and carcinoembryonic antigen (CEA). CCSST was confirmed with cytogenetic analysis showing the translocation associated with EWSR1-ATF1 fusion gene. Therefore, ductal differentiation is a unique finding that should be considered when evaluating for CCSST.

Clear cell lesions in pathology: Histomorphologic approach to diagnosis

There has been remarkable progress in the field of surgical pathology; however, histomorphology has remained the most important and essential tool of the surgical pathologist in everyday practice till now. It is surprising that the hematoxylin-eosin (H and E) stain, introduced more than a century ago, has still remained the gold standard stain for histological examination and diagnosis of human diseases. Besides different findings or clues observed in histopathology sections like inclusions, granules, grooving, globules, halo, or clearing, which would enable the pathologist to provide a precise and accurate diagnosis; observation of clear cells is one of the important findings and clue for reporting. It may also sometimes lead to difficulties and delays in establishing the diagnosis. It can be focal or extensive and primary or rarely it may be secondary. Clear cell changes may be observed in many non-neoplastic, benign, or malignant tumors of diverse origin. Clear cell tumors contain a preponderance of clear cells. It can be seen in almost all the organs of human body and can be classified according to location or biological behavior. Commonly seen clear-cell tumors are usually malignant and common organs involved are female genital tract, urogenital tract, head and neck areas, central nervous system, skin, and rarely in bone and soft tissues. For approach to clear cell lesions, one has to decide if the change is artifactual, a mimic of clear cell tumors, or a clear cell tumor in reality. Once the mimics and artifactual/degenerative changes have been ruled out, a tumor either primarily of clear cell origin or showing secondary change has to be decided. The tumor next is to be diagnosed as benign/malignant and epithelial/mesenchymal based on morphology.

PTCH1 Mutation in a Patient With Metastatic Undifferentiated Carcinoma With Clear Cell Change

Clear cell basal cell carcinoma (BCC) is an unusual variant of BCC. Its pathogenesis, prognosis, and optimal management remain poorly described due to its rarity. This report presents a 51-year-old man with a history of excised BCC and cutaneous squamous cell carcinomas of the face, with multiple recurrent poorly differentiated carcinomas with clear cell changes of the shoulder for which further classification using conventional histologic means was not possible. His tumor tissue was sent to Foundation Medicine for testing, which revealed a high number of pathogenic genomic alterations, including a mutation inPTCH1. He was diagnosed with dedifferentiated BCC and started on vismodegib. He developed lung metastases while receiving vismodegib, and his disease continued to progress while he was undergoing treatment in a phase I clinical trial. Given the high number of pathogenic alterations suggestive of high tumor mutational burden, immunotherapy was considered and off-label authorization was obtained for treatment with a PD-1 antibody (pembrolizumab). He had a dramatic disease response after 4 infusions of pembrolizumab. Molecular testing was instrumental in determining the correct diagnosis and formulating appropriate treatment options for this patient. Molecular profiling of metastatic BCCs and its subtypes is essential to the development of effective targeted therapies and combination approaches.

Pagetoid Dyskeratosis of the Male Genitalia: Case Report and Review

Pagetoid dyskeratosis is a benign incidental pathologic finding that has been reported in many distinct skin lesions on various locations of the body. A man who had pagetoid dyskeratosis within lesions of the penile shaft is described and similar cases of pagetoid dyskeratosis in lesions of the male genitalia are reviewed. The patient was a 26-year-old healthy man who developed several asymptomatic penile papules that were refractory to topical imiquimod 5% cream and cryotherapy. Snip biopsies were performed and microscopic examination revealed pagetoid dyskeratosis. PubMed was searched for the following terms: cell, clear, dyskeratosis, genitalia, pagetoid, penile, penis, prepuce, scrotum, and shaft. The papers containing these terms and their references were reviewed. Pagetoid dyskeratosis has been observed in lesions on the prepuce and scrotum; this case report now expands the distribution of this finding to the penile shaft. Clinicians and pathologists should be aware of this intriguing potential incidental finding within skin lesions of the male genitalia.

Seborrheic Keratosis With Prominent Clear Cell Changes-A Rare But Important Diagnostic Variant

Seborrheic keratoses, although exceedingly common, occasionally have morphologic similarities to other lesions that complicate a typically straightforward diagnosis. The authors present a case of a 69-year-old man with a left shoulder lesion that displayed characteristic clinical and microscopic features of seborrheic keratosis on biopsy. However, diffuse and prominent clear cells were also noted. These stained strongly with Periodic acid-Schiff and were diastase sensitive, suggestive of glycogen accumulation and possible trichilemmal differentiation. This case is presented to demonstrate a unique and striking example of clear cell change within a seborrheic keratosis and to briefly review the published literature on this finding, which is rarely reported and demands close examination to exclude more aggressive neoplasms.

Primary clear cell sarcoma of the head and neck: a case series with review of the literature

BACKGROUND

Clear cell sarcoma typically arises in deep soft tissues of the foot/ankle. Primary head and neck clear cell sarcoma is rare. We report three molecularly confirmed primary head and neck clear cell sarcoma and review the literature.

METHODS

Head and neck clear cell sarcoma with no primary elsewhere were retrieved from archival/consultation files. English language literature review of all reported head and neck clear cell sarcoma was performed.

RESULTS

Three cases were identified. The tumors, all in men, presented on the scalp of a 33-year-old, face of a 20-year-old and tongue of a 44-year-old. Tumors ranged from 0.6 to 1.4 cm. All had typical features of clear cell sarcoma, including nests of tumor cells divided by fibrous septae. One had multinucleated wreath-like giant cells. One had a focal junctional component. Immunohistochemistry was positive for S100 (three out of three), HMB45 (three out of three) and Melan-A (two out of three). All had EWSR1 rearrangements by fluorescence in situ hybridization. Follow up available for one patient revealed no evidence of disease after wide excision and radiation. Seven additional reported cases were identified and tabulated.

CONCLUSION

Head and neck clear cell sarcoma is rare but should be considered in the differential diagnosis of nested tumors with fibrous septae. Molecular analysis should be considered for definitive diagnosis regardless of location.

Basal cell carcinomas showing histological features generally associated with cutaneous adnexal neoplasms

Basal cell carcinoma (BCC) is the commonest malignant neoplasm in humans. Although a histopathological diagnosis of BCC is straightforward in the vast majority of cases, unusual histological variants can present a diagnostic challenge. A small proportion of BCCs show features which are generally associated with cutaneous adnexal neoplasms. Such changes may involve either the epithelium or the stroma and can mislead the pathologist particularly in small biopsies. Despite the growing evidence which speculate that BCC is a primitive follicular tumor, it is unusual to encounter tumors which actually show definitive signs of adnexal differentiation. This review aims to address this somewhat overlooked aspect of a very common tumor and offers practical guidance to distinguish them from adnexal neoplasms which they might mimic.

Clear cell proliferations of the skin

Clear cell proliferations of the skin consist of a diverse group of lesions characterized by the presence of cells with abundant clear cytoplasm. They may arise from primary, metastatic, or non-neoplastic origins, with their distinctive cytoplasmic clearing attributable to causes ranging from artifact to accumulation of materials such as glycogen, mucin, or lipids. Despite the heterogeneity of these lesions, their distinguishing characteristics may be subtle, especially at high power. As such, histologic diagnosis can be challenging, and proper consideration relies on an understanding of the scope of possible origins, etiologies, and key immunohistochemical staining patterns of the various entities. This review categorizes cutaneous clear cell neoplasms by histogenesis, and offers differential diagnostic strategies to aid in their clinicopathologic evaluation.

Clear Cell Melanoma: A Cutaneous Clear Cell Malignancy

Clear cell melanoma is a rare clear cell malignancy. Accurate diagnosis of clear cell melanoma requires integration of immunohistochemical and morphologic findings, with molecular studies to rule out clear cell sarcoma. The differential diagnosis includes melanoma, carcinoma, perivascular epithelioid cell tumor, and epidermotropic clear cell sarcoma. We use a case of a lesion on the helix of an 86-year-old man as an example. Histologic examination revealed an ulcerated clear cell malignant tumor. Tumor cell cytoplasm contained periodic acid-Schiff–positive, diastase-sensitive glycogen. Tumor cells showed positive labeling for S100, HMB-45, and Melan-A, and negative labeling for cytokeratins, p63, and smooth muscle actin. Molecular studies demonstrated BRAF V600E mutation, copy gains at the 6p25 (RREB1) and 11q13 (CCND1) loci, and absence of EWSR1-ATF1 fusion. These findings supported a diagnosis of clear cell melanoma. The rare pure clear cell morphology occurs due to accumulation of intracytoplasmic glycogen. We review the differential diagnosis of clear cell melanoma and describe the utility of immunohistochemical and molecular studies in confirming this diagnosis.

Primary cutaneous perivascular epithelioid cell tumor: a clinicopathological and molecular reappraisal

BACKGROUND

Perivascular epithelioid cell tumor (PEComa) is a rare neoplasm of uncertain histogenesis with a mixed myomelanocytic immunophenotype, rarely arising in the skin (primary cutaneous PEComa [pcPEComa]).

OBJECTIVE

We analyzed the clinicopathological features of 8 pcPEComas, assayed for DNA copy number changes and for initiating mutations common in melanocytic neoplasms.

METHODS

pcPEComas were evaluated using immunohistochemistry, comparative genomic hybridization, and DNA sequencing.

RESULTS

pcPEComas were erythematous nodules, mostly in the lower extremities of women (5/8), composed of large pale-staining epithelioid cells. The patient's age range was 26 to 67 (mean 46) years. The percentages of tumors staining positively were as follows: micro-ophthalmia-associated transcription factor, NKI/C3, bcl-1, E-cadherin, and cathepsin K (100%); HMB-45, 4E-binding protein 1, and CD68 (88%); smooth muscle actin and muscle-specific actin (40%); S100 (38%); calponin (20%); desmin (13%); and melan-A, SOX10, and keratin (0%). No chromosomal copy number changes or initiating mutations were identified.

LIMITATIONS

Small sample size is a limitation.

CONCLUSIONS

pcPEComas have a different molecular signature than extracutaneous tumors and are unrelated to tuberous sclerosis. However, the common expression of 4E-binding protein 1 points to a role of the mTOR pathway in their pathogenesis. Because pcPEComas are diagnostically challenging, we propose that micro-ophthalmia-associated transcription factor, NKIC3, smooth muscle actin, desmin, bcl-1, cathepsin K, and 4E-binding protein 1 can be used when evaluating a possible pcPEComa.

Eruptive dermal clear cell desmo-plastic mesenchymal tumors with perivascular myoid differentiation in a young boy. A clinical, histopathologic, immunohistochemical and electron microscopy study of 17 lesions

Clear cell tumors of the skin are observed in a wide variety of benign and malignant conditions with different histogenesis, sharing the presence of cells with abundant clear cytoplasm. Herein, we report the clinicopathologic features of a healthy young patient affected by asymptomatic, eruptive and disseminated, benign clear cell dermal tumors since early infancy. Neither family history nor genetic testing and counseling provided further useful information. The lesions were mostly confined to the face and lower left extremity with pink teleangiectatic papules and small nodules. Over a 4-year period, a total of 16 different cutaneous lesions were biopsied and histopathologic and immunohistochemical studies carried out; an additional lesion was also removed for electron microscopy examination. Histopathology evidenced multiple perivascular growths of spindle to oval and round cells intermingled with clear/granular cells throughout the dermis, with prominent desmoplasia and numerous capillary-like vessels with focal hemangiopericytoma-like features. Immunohistochemical neoplastic cells were uniformly positive for h-caldesmon and focally smooth muscle α-actin and CD13 indicating myoid differentiation whereas the consistent diffuse cytoplasmic staining for lysosome antigen, such as CD68PG-M1 and NKI/C3 along with the ultrastructural findings supported the view of a lysosome-mediated apoptotic process. The differential diagnosis with other clear cell cutaneous neoplasms is discussed.