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.

Adipophilin expression in skin lesions with clear cell histology

AIMS

Clear cells formed due to depositions of glycogen or lipids in the cytoplasm commonly occur in various tissues. Adipophilin (ADP), a lipid regulatory protein, is closely related to lipid droplets. This study aims to examine adipophilin expression in clear cells of various skin lesions.

METHODS

ADP expression was examined using immunohistochemistry in 108 sections from 15 skin lesion types with clear cell histology, namely, sebaceoma (n=16), sebaceous adenoma (n=3), sebaceous carcinoma (n=12), xanthomata cutis (n=10), xanthogranuloma (n=8), Paget's disease (n=10), Bowen disease (n=10), hidradenoma (n=9), atypical lipoma (n=5), superficial lipomatous nevus (n=5), metastatic renal cell carcinoma (n=5), squamous cell carcinoma (n=4), seborrheic keratosis (n=4), dermatofibroma (n=4) and clear cell sarcoma (n=3).

RESULTS

ADP was not expressed in Bowen disease, hidradenoma or seborrheic keratosis. Four expression patterns, foamy, reticular, granular and punctate, were summarised based on their expression in clear cells. Different expression patterns were related to tissue origin and differentiation degree. Foamy expression was commonly observed in lesions with mature sebaceous glands and xanthomas; reticular expression in adipocytes; granular expression in xanthoma, xanthogranuloma and metastatic renal carcinoma and punctate expression in sebaceoma, sebaceous carcinoma, Paget's disease, squamous cell carcinoma and clear cell sarcoma. Furthermore, stronger staining with focal vesicular labelling was noted in sebaceoma than in sebaceous carcinoma. Characteristic labelling was noted, including the circular distribution in Touton giant cells of xanthogranulomas and focal distribution in the clear cells along the edge of necrotic tissue in clear cell sarcoma.

CONCLUSIONS

ADP is useful in identifying intracytoplasmic lipids and can be used to diagnose skin lesions with clear cell histology, especially in some lesions with characteristic labelling.

Comparison of adipophilin and recently introduced PReferentially expressed Antigen in MElanoma immunohistochemistry in the assessment of sebaceous neoplasms: A pilot study

BACKGROUND

We and others have noticed consistent staining of sebaceous glands with PReferentially expressed Antigen in MElanoma (PRAME). We aimed to determine whether PRAME was as sensitive, specific, and interpretable as adipophilin for distinguishing sebaceous neoplasms (SNs) from other neoplasms.

METHODS

Twenty SNs and 32 control cases were stained for PRAME and adipophilin. Extent of staining was scored as follows: 0, no staining; 1, <5% positivity; 2, 5% to 50% positivity; and 3, >50% positivity. Intensity was scored as negative, weak, moderate, or strong. A composite score was determined by adding the scores for extent and intensity.

RESULTS

PRAME had positive composite scores in all 20 SNs in the more differentiated areas, whereas adipophilin had positive composite scores in 19/20 cases. PRAME showed positivity in the basaloid cells in 15/16 cases, whereas adipophilin was positive in 14. Among controls, PRAME and adipophilin had positive composite scores in 3/32 cases and 6/32 cases, respectively.

CONCLUSIONS

PRAME and adipophilin are comparable in terms of distribution and intensity for staining sebocytes. In the basaloid cells, PRAME expression is often more diffuse and easier to detect than adipophilin. In comparing the SNs to the controls, PRAME was more sensitive and more specific than adipophilin. PRAME could be used as an additional marker of sebaceous differentiation in everyday practice.

Current review of sebaceous cell carcinoma

PURPOSE OF REVIEW

Periocular sebaceous cell carcinoma is a rare malignancy that is often misdiagnosed leading to increased morbidity and mortality. This review aims to describe current knowledge on the disease to aid clinicians in timely diagnosis and treatment.

RECENT FINDINGS

New research has shown that the diagnosis of sebaceous cell carcinoma can be aided with immunohistochemical stains. A revision in the American Joint Committee on Cancer staging system incorporates new tumor size classifications in the staging of eyelid carcinomas. Wide local excision and Mohs micrographic surgery continue to represent the standard of care for initial treatment of localized disease.

SUMMARY

The current review highlights diagnostic and treatment modalities to allow clinicians to make timely diagnosis and tailor treatment plans for individual patient presentations.