Desmoplastic trichoepithelioma is an exceptional, benign adnexal tumefaction arising from basal cells of outer root sheath of the hair follicles. With an estimated incidence of 1 : 5000, desmoplastic trichoepithelioma commonly appears in young and middle aged women, demonstrates a female preponderance and usually appears within 8 years to 81 years 12.

Multiple foci of preliminary lesions of desmoplastic trichoepithelioma can concur with foci of basal cell carcinoma, thus indicating a concomitant genetic predisposition. As a tumefaction delineating an autosomal dominant mode of disease inheritance, desmoplastic trichoepithelioma can be associated with basal cell carcinoma or a cylindroma. Association of cylindroma with desmoplastic trichoepithelioma demonstrate concurrent mutations within the CYLD gene. Nevertheless, absence of CYLD genomic mutation indicates mutant functioning of alternative genes in the emergence of desmoplastic trichoepithelioma. Desmoplastic trichoepithelioma predominantly arises within zones of sun exposure and can simulate lesions of basal cell carcinoma 12.

Desmoplastic trichoepithelioma can clinically and histologically recapitulate several benign and malignant conditions such as syringoma, morphea-like basal cell carcinoma (MBCC), microcystic adnexal carcinoma (MAC), conventional trichoepithelioma and adjunctive tumours. Additionally, sebaceous hyperplasia, granuloma annulare, scar tissue, hamartoma, melanocystic nevi, keratosis and cutaneous squamous cell carcinoma require a demarcation. Histological differentiation is mandated from morphea-like basal cell carcinoma (MBCC), microcystic adnexal carcinoma (MAC) and eccrine syringo-carcinoma 56.

Morphea-like basal cell carcinoma (MBCC) or sclerosing basal cell carcinoma is an aggressive, exceptional variant with an atypical clinical representation. It emerges as a solitary, yellowish, pale or flesh coloured, firm, poorly-defined, waxy or scar like, flat or mildly depressed lesion predominantly appearing on the head and neck, face, trunk, limbs and aforesaid lesions clinically and histologically recapitulate benign desmoplastic trichoepithelioma. Basal cell carcinoma preponderantly appears as nodular or superficial. As an aggressive subtype, morphea-like basal cell carcinoma therapeutically necessitates complete surgical excision, in contrast to benign desmoplastic trichoepithelioma. As aforesaid tumours are predominantly composed of follicular germinative cells, several common morphological characteristics can concur 67.

Akin to desmoplastic trichoepithelioma, morphea-like basal cell comprises of infiltrating strands and islands of basaloid and monomorphic epithelial cells embedded within a dense fibrous and sclerotic stroma. Five distinct histological features aid the differentiation of desmoplastic trichoepithelioma from morphea-like basal cell carcinoma such as the occurrence of annular lesions, horn cysts, epidermal hyperplasia, keratin granules and calcification. Enlarged aggregates of tumour cells are frequent in morphea-like basal cell carcinoma and exceptional in desmoplastic trichoepithelioma. Syringoma is a benign, predominantly pubertal, cutaneous adnexal tumour demonstrating ductal differentiation and manifests miniature, asymptomatic, multiple, flesh coloured papules preponderantly situated upon cheeks, lower eyelids or periorbital region 67. On histology, synrigoma delineates multiple eccrine ducts, doubly layered with cuboidal epithelium, scattered within dermal fibrous tissue stroma. Several, engendered tubular articulations are generally confined to the superficial dermis. Features such as narrow cords and strands of basaloid cells, foreign body granulomas and calcification are exceptional in syringomas although frequent in desmoplastic trichoepithelioma 67.

In contrast, predominantly solitary with a lack of ductal differentiation, desmoplastic trichoepithelioma commonly displays horn cysts, calcification, follicular differentiation and elongated epithelial strands. Immune reactivity for cytokeratin 20 (CK20) for Merkel cells and non reactivity for carcinoembryonic antigen (CEA) is nearly comprehensive in desmoplastic trichoepithelioma, a pattern which is reversed in luminal cells of syringoma. Microcystic adnexal carcinoma is an exceptional adnexal neoplasm commonly arising upon centroidal face or head and neck region. A gradually evolving, enlarged, asymmetrical, firm, flesh coloured, indurated, diffuse plaque or nodule with poorly defined perimeter, demonstrating occasional, superimposed telangiectasia and extension into subcutaneous adipose tissue is exemplified 67.

Microcystic adnexal carcinoma (MACs) as an exceptional, cutaneous carcinoma, invades locally and metastasizes infrequently. Indolent, flesh coloured or yellowish, facial lesions of MACs demonstrate basaloid cellular cords and nests embedded within a fibrous tissue stroma. MACs are diffuse lesions, infiltrate the subcutaneous tissue and depict perineural invasion (PNI) in around 80% instances. A singular immune stain segregating trichoepithelioma from a microcystic adnexal carcinoma is absent 67.

Histologically, predominantly proliferating tubular articulations are denominated. In contrast to a benign, indolent desmoplastic trichoepithelioma, microcystic adnexal carcinoma is aggressive and displays significant localized tissue destruction and possible distant metastasis. Superficial extraction of tissue samples can result in misinterpretation of microcystic adnexal carcinoma as a squamous cell carcinoma, syringoma or desmoplastic trichoepithelioma in an estimated 30% instances 67.

Immune reactivity to cytokeratin 20 (CK20), cytokeratin 15(CK15) and cytokeratin 7(CK7), CD10 and BerEp4 can be employed to segregate microcystic adnexal carcinoma from desmoplastic trichoepithelioma although none is confirmatory. Familial instances of MACs can concur with basal cell carcinoma or a papillary carcinoma thyroid.

Cutaneous metastatic breast carcinoma requires distinction from desmoplastic trichoepithelioma. Majority of cutaneous metastasis from carcinoma breast are enunciated following detection of the primary carcinoma. Infrequently, metastasis can be discovered prior to or concurrent with primary breast carcinoma. Breast carcinoma is a malignancy frequently delineating cutaneous metastasis. An estimated 30% of breast cancers exemplify a tendency to metastasize. Common sites of cutaneous metastasis of carcinoma breast are chest and abdomen. Infrequently, metastatic lesions can be cogitated upon scalp, face, neck, upper, extremities, ventral trunk. Rapidly enhancing, asymptomatic, firm, scar - like nodules or facial tumefaction can simulate desmoplastic trichoepithelioma. Nevertheless, cutaneous metastasis from a primary breast cancer requires diagnostic exclusion 57.

Genetic assay delineates non reactive incriminated coding exons of CYLD gene extracted from deoxy ribo nucleic acid (DNA) of peripheral blood lymphocytes of blood relatives. Genetic concurrence betwixt desmoplastic trichoepithelioma, microcystic adnexal carcinoma and basal cell carcinoma requires further evaluation 12.

Desmoplastic trichoepithelioma enunciating foci of perineural invasion can be managed with conservative measures. Alternatively, a comprehensive surgical excision is beneficial and is accompanied by a lack of tumour reoccurrence 78.

Moh’s micrographic surgery can be adopted. Regular follow up and antecedent tissue examination procures an early diagnosis with minimal cosmetic encumbrance. Enlarged lesions with peri-neural invasion mandate an appropriate monitoring to assess clinical behaviour. An aggressive therapeutic approach should be adopted with caution, similar to associated cutaneous carcinomas, especially for treating lesions situated upon cosmetically sensitive lesions 78.

Moh’s micrographic surgery can be adopted for managing desmoplastic trichoepithelioma in order to circumvent tumour reoccurrence and localized tissue invasion as aggressive behaviour is extremely exceptional. Moh’s micrographic surgery is beneficial in treating lesions of atypical histology or appearing in sensitive zones, as the face or areas necessitating tissue sparing surgery. However, micrographic surgery remains an expensive therapeutic option, in contrast to alternative surgical procedures 78.

Therapeutic modalities such as laser surgery, dermabrasion, administration of topical 5% imiquimod, curettage, electrodessication and radio-surgical abrasion can be employed to manage desmoplastic trichoepithelioma, although proportionate reoccurrence is enhanced with aforesaid techniques, as apposed to localized surgical extermination. Majority of superficial tissue samples are accompanied by inferior pathological evaluation. Thus, as aforesaid techniques may not be competent in procuring a histologically adequate tumour margin, evaluation of aggressive tumours simulating desmoplastic trichoepithelioma may not be satisfactory78.

Localized surgical extermination of the lesion is a preferential treatment for a majority of benign tumours. Comprehensive remission with minimal reoccurrence of can be achieved with surgical methods although post- surgical complications such as scarring and hypopigmentation can occur in cosmetically sensitive zones as the face. Classic, definitively benign lesions of desmoplastic trichoepithelioma can be satisfactorily managed with close monitoring, regular follow up and localized surgical excision 78. (Table 1)