A rare case of Trichilemmal Carcinoma: histology and management Lisa Fronek DO, Allyson Brahs BS, Maheera Farsi DO, Richard Miller DO, Dudith Pierre-Victor, PhD, MPH HCA Healthcare USF Morsani College of Medicine: Largo Medical Center Program Western University of Heath Sciences, College of Osteopathic Medicine of the Pacific Introduction Clinical and Histologic Findings Discussion Trichilemmal carcinoma (TC) is a rare, malignant, adnexal neoplasm that is TC is a rare, adnexal tumor with evidence for follicular ORS or trichilemmal derived from the outer root sheath (ORS) of the hair follicle. These tumors differentiation. It is considered the malignant analogue of trichilemmoma. predominantly occur in elderly patients on sun-exposed areas, specifically on Clinical presentation is variable; due to its ability to resemble different clinical the head and neck with the face defined as the most common location. The entities, the diagnosis of TC relies on histological evaluation, accompanied by mean age of diagnosis is 70 years old with a slight male predominance. IHC. Microscopically, TC features a solid, lobular, or trabecular growth pattern These lesions are commonly identified as a papular, nodular, and sometimes, often centered around a pilosebaceous unit. The tumor cells are clear, exophytic. They generally arise de-novo, but may also derivate from an polygonal, and glycogen-rich (periodic acid-Schiff positive (PAS), diastase underlying proliferating trichilemmal cyst with a loss of p53, a seborrheic sensitive), reminiscent of clear cells of the ORS. It exhibits peripheral keratosis, a nevus sebaceous, or a scar. They can be locally aggressive and palisading of basaloid cells abutting a sometimes thickened hyalinized may exhibit telangiectasias and ulceration due to local destruction. basement membrane. Upon closer inspection, cytologic atypia, nuclear pleomorphism, prominent nucleoli, and a high mitotic index can be seen. While the clinical differential diagnosis commonly includes basal cell CD34 stains the external layer of the ORS without labelling the rest of the carcinoma (BCC), squamous cell carcinoma (SCC), and keratoacanthoma, 1 2A follicle, so it can be used to suggest outer sheath differentiation. Ki-67 and the histopathological differential also includes trichilemmoma, p53 labelling can be used to support the malignant nature of a suspected TC. trichoepithelioma, clear cell SCC, clear cell porocarcinoma, and clear cell Though it appears to be cytologically malignant under the microscope, TC hidradenocarcinoma. The main differentiating histological feature in a TC is typically demonstrates nonaggressive clinical behavior. Wide local excision the evidence of trichilemmal keratinization, where the tumor exhibits an with histological demonstration of clear margins has traditionally been the absence of granular layer between the stratum spinosum and stratum treatment of choice. Anecdotal reports equate the risk of recurrence and corneum. The standard of treatment for TC is wide local excision (WLE) with lymph node metastasis to that of SCC, and therefore, TC is treated tumor free margins, however, there has been increasing evidence for the accordingly. Surgical margins generally emulate the 4-6 mm standard margins efficacy of Mohs micrographic surgery (MMS) in recent years. for SCC, though a few authors suggest utilizing safety margins greater than 1 cm. MMS has been increasingly employed for numerous rare adnexal tumors including TC, and was under consideration for this case as well. Case Report Conclusion Here we present a case of a 66-year-old Caucasian male who presented to 2B 2C TC is a rare adnexal tumor that grossly and microscopically mimics several the dermatology clinic for a routine full body skin exam and was diagnosed entities. A biopsy is essential for diagnosis and often requires supplemental with a biopsy proven TC. The patient had a history of actinic keratoses immunostaining. It should be distinguished from other tumors of follicular treated with topical 5-fluorouracil (5-FU) and BCCs status-post excision and origin and from other cutaneous malignancies. Complete excision with tumor- MMS. On physical exam, there was a pink to erythematous, pearly plaque free margins is the typical treatment modality, though, MMS has some with arborizing telangiectasia and fine scale located on the right central advantages, including comprehensive visualization of the margins and a anterior neck; no ulceration, discharge, or lipid deposits were noted (Figure greater preservation of healthy tissue. As we struggle for uniformity in 1). Tangential shave biopsy was performed of the lesion and histopathologic treatment recommendations, the therapeutic modality and surgical margins report revealed an adnexal neoplasm with trichilemmal differentiation, should be decided on an individual basis considering the patient’s preference desmoplastic component and atypia with margins involved (Figures 2A-B). and the lesion’s clinicopathologic features. Further characterization of the Immunohistochemical staining (IHC) was positive for CD34, and tumor cells true nature and behavior of TC would contribute to a standard treatment displayed uptake of the Ki-67 proliferation marker; staining for p53 was recommendation. negative (Figure 3A-B). The differential diagnoses, as described by the pathologist, included the favored diagnosis of a well-differentiated TC versus References desmoplastic trichilemmoma with atypia. We discussed with the pathologist 3A 3B Chai MK, Tenzel P, Iacob C, Jordan A, Reddy HS. Eyelid Trichilemmal Carcinoma. Saudi J Ophthalmol. about differentiating these two entities, and it was decided that the cytologic 2017;31:183-5. [PMID: 28860920]. atypia and pleomorphism outweighed only a small focus of desmoplastic Figure 1. Pink to erythematous atrophic plaque with arborizing telangiectasias on the right Kim YH, Lee YK, Choi KW, Lee CY, Kim KH. A Case of Trichilemmal Carcinoma Treated with Mohs anterior neck (labeled in the image as B). Micrographic Surgery. Ann Dermatol. 2008;20:157-61. [PMID: 27303183]. change; therefore a diagnosis of TC was heavily favored. The pathologist Hamman MS, Brian Jianq SI. Management of trichilemmal carcinoma: an update and comprehensive review advised for complete removal of the lesion with further evaluation. The Figure 2. (A) Hyperkeratosis, variable parakeratosis and focal pagetoid spread in the of the literature. Dermatol Surg. 2014;40:711-7. [PMID: 25111341] patient deferred MMS in favor of WLE and was treated successfully with 3 epidermis. (B) The dermis contains a clear cell infiltrate, intracytoplasmic eosinophilic Tolkachjov SN, Hocker TL, Camilleri MJ, Baum CL. Mohs micrographic surgery in the treatment of trichilemmal carcinoma: the Mayo Clinic experience. J Am Acad Dermatol. 2015;72:195-6. [PMID: mm margins. The final pathology report identified no residual adnexal inclusions, peripheral palisading along a thickened basement membrane, surrounded by 25497926]. neoplasm and an incidental superficial BCC with free margins. lymphocytic infiltrate (H&E, 4x). (C) Evidence of nuclear pleomorphism, abundant polygonal Takata M, Rehman I, Rees JL. A trichilemmal carcinoma arising from a proliferating trichilemmal cyst: the loss cells with clear cytoplasm and scattered inclusion bodies, small focus of desmoplastic of the wild-type p53 is a critical event in malignant transformation. Hum Pathol. 1998;2:193-5. [PMID: 9490283]. change, (H&E, 10x). Chapter 31: Tumors of the hair follicle. In: McKee’s Pathology of the Skin: with Clinical Correlations. Calonje Figure 3. Immunohistochemical Staining (IHC) was positive for CD34 (A) and Ki-67 (B), but E, Brenn T, Lazar AJ, Billings SD. 5th ed. Elsevier; 2019. p. 1545-88. Tolkachjov SN. Adnexal Carcinomas Treated With Mohs Micrographic Surgery: A Comprehensive Review. negative for p53 (not pictured). Dermatol Surg. 2017;43:1199-207. [PMID: 28445202].

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