fibroepithelioma of Pinkus, case1

FIBROEPITHELIOMA (PINKUS)

Fibroepitheliomas are characterized by the intermingling of primordial follicular (basaloid) epithelium, as well as more mature follicular epithelium, with nodular collections of stroma. The epithelium forms arcuate bands of varying width that sweep around the stromal aggregates. Epidermal connections are common, and the epidermal component can be of superficial multicentric basal cell carcinoma type, particularly at the periphery. Neither well-formed hair bulbs, sebaceous components, apocrine components, nor the features of a highly organized and well-differentiated follicular hamartoma are seen in the classical fibroepithelioma. Fibroepitheliomas are usually found somewhere between the navel and the knees.

Pinkus indicated fibroepitheliomas are basal cell carcinoma precursors. Most textbooks, as well as articles in the recent literature, indicate fibroepithelioma is simply a basal cell carcinoma variant at the outset. This is in spite of the facts that the location differs markedly from ordinary basal cell carcinomas and that aggressive behavior is exceptional.

The stroma is of follicular fibrous sheath type and has the same features as those seen in fibroepithelial follicular and folliculosebaceous hamartomas such as fibrofolliculoma, perifollicular fibroma, and folliculosebaceous cystic hamartoma. The interconnecting, thin strands of epithelium resemble those found in fibrofolliculomas to a remarkable degree. Primordial follicular epithelium is sometimes attached to eosinophilic epithelium resembling follicular infundibular or isthmic epithelium in a radial fashion similar to that found in some benign follicular tumors. These findings raise the possibility that the fibroepithelioma is initially a fibroepithelial follicular hamartoma with limited epithelial follicular differentiation rather than being an aggressive basal cell carcinoma from the outset. The basaloid epithelial component is not unlike that found in pseudocarcinomas as seen in some dermatofibromas and some examples of nevus sebaceus of Jadassohn.

The steps involved in the development of locally aggressive basal cell carcinomas from fibroepitheliomas have not been delineated, and the frequency of this neoplastic transformation is unknown.

Focal deposition of amyloid is seen in the stroma in this case and is of no known significance. Amyloid is occasionally found in basal cell carcinomas and trichoblastomas, particularly within those having a an infundibular epithelial component.

An indolent papule from the scrotum of a 70 year old male:

A composite scan power view showing anastomosing bands of epithelium separated by large amounts of stroma. The stroma accounts for over 50% of the total volume of the tumor.

Another composite scan power view. This is from a section taken parallel to the one above. The strands of epithelium are generally more delicate than those seen above.

A composite low power view from the section shown above. Note the delicate bands of epithelium that arch and anastomose in the more superficial part of the section. The broader bands of epithelium in the deep part of the picture are composed of cells having eosinophilic cytoplasm in some areas but are more basaloid in others. The abundant stroma is paucicellular. The delicate strands of epithelium resemble those seen in fibrofolliculomas. The epithelium having more voluminous cytoplasm resembles infundibular or isthmic epithelium.

A high power view of the deepest nest of epithelium in the picture shown above. Peripheral palisading of nuclei is associated with a cleft between the epithelium and the delicately fibrillar, slightly basophilic stroma. This clefting resembles that seen in basal cell carcinomas.

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	A composite scan power view showing anastomosing bands of epithelium separated by large amounts of stroma. The stroma accounts for over 50% of the total volume of the tumor.
	Another composite scan power view. This is from a section taken parallel to the one above. The strands of epithelium are generally more delicate than those seen above.
	A composite low power view from the section shown above. Note the delicate bands of epithelium that arch and anastomose in the more superficial part of the section. The broader bands of epithelium in the deep part of the picture are composed of cells having eosinophilic cytoplasm in some areas but are more basaloid in others. The abundant stroma is paucicellular. The delicate strands of epithelium resemble those seen in fibrofolliculomas. The epithelium having more voluminous cytoplasm resembles infundibular or isthmic epithelium.
	A high power view of the deepest nest of epithelium in the picture shown above. Peripheral palisading of nuclei is associated with a cleft between the epithelium and the delicately fibrillar, slightly basophilic stroma. This clefting resembles that seen in basal cell carcinomas.