Trichilemmal carcinoma, an uncommon tumor: update on its management and prognosis

Introduction: Trichilemmal carcinoma (TC) is a rare neoplasm of skin appendages. It was first described in 1968 as tricoleptocarcinoma, and has an incidence of 0.05% in patients subjected to histopathological examination after excision of cutaneous lesions. TC has an indolent clinical course ; however, reports in the literature put in doubt this indolent behavior . Objectives: To provide an update on the management and prognosis of TC. Methods: A search of the PubMed and SciELO databases by using with the MeSH terms “trichilemmal carcinoma”, “tricholemmal carcinoma”, “adnexal skin tumor”, and “carcinoma triquilemal” was performed. Results: Owing to the rarity of TC, most studies were case reports, which essentially corroborate the indolent nature of the disease. Surgical excision is the recommended treatment, and is associated with a low risk of recurrence and low morbidity and mortality. Conclusion: The behavior of the lesion and the procedure of treatment of TC are based on isolated cases or in a small series of cases. Because of its low prevalence, a multicenter collaboration of a greater number of cases can help define the best treatment recommendations, pathophysiology, and prognosis. Surgical excision remains the gold standard of treatment, and is associated with a low risk of recurrence. ■ ABSTRACT


INTRODUCTION
Trichilemmal carcinoma (TC) is a rare neoplasm of the skin appendages, originating from the external root sheath of hair follicles.TC occurs primarily in sun-exposed skin areas such as the scalp, forehead, neck, torso and upper limbs, usually among elderly individuals, predominantly in women 1 .
It was first described in 1968 as tricoleptocarcinoma, and occurred in 0.05% of patients that were subjected to histopathological examination of excised cutaneous lesions 2 .Headington was the first to propose the term TC in 1976 to describe a "histologically invasive, cytologically atypical clear cell neoplasm of adnexal keratinocytes which is in continuity with the epidermis and/or follicular epithelium" 3 .
It seems to be an indolent tumor; however, reports in literature put in doubt this indolent behavior.

OBJECTIVE
The objective of this report was to provide an update on the management and prognosis of patients with TC through a literature review.
Differential diagnosis includes benign tricholemmal cyst, squamous cell carcinoma (Figures 2 and  3), basal cell carcinoma, keratoacanthoma, verrucous cysts, proliferative trichilemmal cysts, and pseudocarcinomatous cysts 5,12 .The malignant portion of trichilemmoma seems to originate from the outer layer of the hair follicle 13 .Histologically, TC seems to be an intermediate-to high-grade neoplasia, and represents a lobular proliferation centered on the pilosebaceous unit and composed of clear and pale cells with atypia, containing glycogen with basilar invasion or total thickness of the interfollicular epidermis 14 .The growth of the tumor is lobular and infiltrative, with the lobules frequently centered and expanding the pilosebaceous unit.The initial intraepithelial impairment may extend to the reticular dermis.Actinic damage has been reported as a common feature 11 ; nevertheless, there are reports of tumors in areas without sun exposure.No criterion for universal histopathological diagnosis has been established for TC 15 .
The prognosis depends on the size of the tumor and the location, the degree of differentiation, and the histological subtype.In an analysis of 615 patients with squamous cell carcinomas (with behavior similar to TC), the key prognostic factors for metastasis were increase in tumor depth (> 2 mm), immunosuppression, lesion in the ear, and increased superficial diameter (> 6 mm) 16 .
Despite its aggressive cytological appearance, TC represents an indolent tumor that usually evolves with a benign course and is associated with good clinical prognosis 3 and nonmetastatic potential 16,17 .
However, there are several studies in literature reporting TCs with an aggressive course, with local lymph node invasion 9,18,19 , recurrence 19 , and even metastasis 20,21 , and thus, the actual behavior of the lesion is questionable.In a recent series of 26 patients, survival at 5 years was 89.5% 5 .There is no standardized chemotherapy treatment for TC, but in reports of patients with recurrent tumors or metastases, regimes including cisplatin, cyclophosphamide, and adriamycin (similar to the one used for patients with advanced cases of squamous cell carcinoma) have shown control of tumor growth; however, cure was not attained 5,19 .
Similar to information on the course of the lesion, there are discrepancies in the literature regarding the treatment of TC.Complete surgical excision with histological documentation of free margins is recommended as the standard treatment by some authors 4 , which can be obtained using Mohs micrographic surgery 19 .Others, however, recommend a wide surgical excision 18 .
Adjuvant radiotherapy is requested for high-risk cases, when complete resection is impossible, or in cases of recurrence or metastasis 22 .

CONCLUSION
We can conclude that most of the information on the behavior and approach of the treatment of TC are based on isolated cases or small series of cases.Owing to the low prevalence of these tumors, larger and prospective studies are required to delineate the actual behavior of this lesion, since the behavior differs substantially from the indolent behavior, as described by a large number of authors.
Surgical excision with 1 cm margin is safe and simple, and is associated with a low risk of recurrence.It is important to discuss and warn the patient about the possibility of recurrence and, in cases of recurrent or aggressive tumors, multidisciplinary follow-up, including close liaison with the oncologist for adjuvant treatment, is essential.

Figure 1 .
Figure 1.Clinical aspect of the lesion in the scalp of a 54-year-old woman, with one-year progression.Biopsy revealing a trichilemmal carcinoma.

Figure 2 .
Figure 2. Friable, ulcerated lesion, of about 3 years of progression, in the scalp of a 71-year-old male patient.Histopathological analysis showing malignant proliferative trichilemmal tumor with squamous degeneration area (ulcerated area between 10 and 11 hours).

Figure 3 .
Figure 3.The surgical resection specimen of the lesion of Figure 2 (10 cm ruler for comparison).