Basaloid Follicular Hamartoma

Updated: Feb 06, 2015
  • Author: Kara Melissa T Torres, MD, DPDS; Chief Editor: Dirk M Elston, MD  more...
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Overview

Background

Basaloid follicular hamartoma (BFH) is a rare, benign adnexal tumor. A variety of clinical patterns have been noted with identical histopathologic features and possible associations with numerous disorders. The tumor is morphologically similar to infundibulocystic basal cell carcinoma. [1]

In general, basaloid follicular hamartomas occur in two forms: hereditary and acquired. Hereditary types of basaloid follicular hamartoma can be either generalized or localized. Acquired types of basaloid follicular hamartoma can be localized, solitary, or multiple.

Hereditary basaloid follicular hamartomas

Generalized basaloid follicular hamartoma syndrome (GBFHS) subtype is inherited in an autosomal dominant pattern and has additional cutaneous features that include milia, comedonelike lesions, alopecia or hypotrichosis, and hypohidrosis. The syndrome is usually associated with some autoimmune disease, [2, 3, 4] but widespread lesions with no associated systemic disorders also have been reported. [2] When multiple basaloid follicular hamartomas are associated specifically with myasthenia gravis and diffuse alopecia, the syndrome is known as Brown-Crounse syndrome. [5]

Linear unilateral basaloid follicular hamartoma (LUBFH) subtype is also known as linear unilateral basal cell nevus with comedones, linear unilateral basal cell nevus, and basal cell and linear unilateral adnexal hamartoma. [6] The lesions associated with linear unilateral basaloid follicular hamartoma occur along the lines of Blaschko in a limited, mosaic pattern. [2, 7]

Familial multiple basaloid familiar hamartoma type of is an autosomal dominant disease that may or may not have the clinical features of hypotrichosis, hypohidrosis, and palmoplantar pitting. [2, 8, 9]

Other hereditary syndromes are recognized. Multiple basaloid follicular hamartomas have been reported to be associated with the nevoid basal cell carcinoma syndrome (NBCCS), also known as Gorlin syndrome or basal cell nevus syndrome, [10] and Bazex-Dupré-Christol syndrome. [11] Unilateral and segmentally arranged basaloid follicular hamartomas are associated with Happle-Tinschert syndrome. [12, 13]

Acquired basaloid follicular hamartomas

Solitary/localized lesions are the usual presentations of acquired basaloid follicular hamartoma.

There are few reported cases of multiple basaloid follicular hamartomas with no evidence of autosomal dominance inheritance [11, 14, 15, 16, 17] and nonfamilial systematized unilateral epithelial nevus. [11, 17]

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Pathophysiology

Basaloid follicular hamartoma (BFH) is considered an abortive growth of secondary hair germs, with differentiation limited to the upper part of the follicles. [18]

The causative gene for this hamartoma is still unknown. Deregulation of the sonic hedgehog (SHH) signaling pathway, which is central to the pathogenesis of basal cell carcinoma (BCC), with increased Gli-1 transcription, has been implicated in its pathogenesis. [19, 20, 21] Genetic studies have implicated a patched (PTCH) gene mutation on band 9q23. [19, 22] The levels of PTCH mRNA were found to be significantly lower in basaloid follicular hamartoma compared with basal cell carcinoma, suggesting that the magnitude of SHH signaling strongly influences tumor phenotype. [20, 22]

Basaloid follicular hamartoma may be histologically identical to infundibulocystic basal cell carcinoma. In addition to findings on hematoxylin and eosin (H&E) staining, both entities were found to have positive CK20 staining, suggesting that basaloid follicular hamartoma and infundibulocystic basal cell carcinoma might actually represent the same lesion. [1]

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Epidemiology

Frequency

Both hereditary and nonhereditary forms of multiple basaloid follicular hamartoma (BFH) and linear unilateral basaloid follicular hamartoma (LUBFH) are very rare. No records describe an annual incidence or prevalence for basaloid follicular hamartoma. Sporadic cases are observed, but must be differentiated from infundibulocystic basal cell carcinoma (BCC). The incidence may be underappreciated in the general population, given its limited distribution and benign nature.

Race

Basaloid follicular hamartoma (BFH) has been reported worldwide in people of various races and ethnic backgrounds, including Latin Americans, [8] African Americans, [9] East Asians, [3] Egyptians, [2] and whites.

Sex

Hereditary basaloid follicular hamartoma

Reported cases of multiple basaloid follicular hamartomas (BFHs) associated with systemic lupus erythematosus (SLE) or myasthenia gravis involve only female patients. [3, 5, 21, 23, 24, 25, 26, 27] Other presentations of hereditary and nonhereditary multiple basaloid follicular hamartoma appear to be equally distributed between men and women.

Acquired basaloid follicular hamartoma

In a report describing 56 patients, basaloid follicular hamartoma was documented most frequently in middle-aged or elderly women. [28]

Age

Hereditary basaloid follicular hamartoma

The age of onset of basaloid follicular hamartoma (BFH) varies considerably. [7, 8, 9, 22, 28, 29]

For multiple basaloid follicular hamartomas associated with autoimmune disease, the onset typically occurs in early adulthood, ranging in age from 20-33 years. Most patients showed onset of basaloid follicular hamartoma simultaneously with or soon after the diagnosis of an autoimmune disease was established. [3, 5, 21, 23, 24, 25, 26, 27]

For linear unilateral basaloid follicular hamartoma (LUBFH), the majority of reported patients displayed basaloid follicular hamartoma at birth or in early childhood. [30, 31] Rarely, the onset of lesions has been documented as late as the second decade of life. [32, 33]

Acquired basaloid follicular hamartoma

Lesions typically manifest later in life. Published cases report the age of onset ranging from 20-88 years, with a median of 66 years and a mean of 63 years. [28]

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Prognosis

The prognosis for basaloid follicular hamartoma (BFH) is usually excellent, unless associated systemic disorders and/or basal cell carcinoma (BCC) develop. Basaloid follicular hamartomas are generally benign, superficial, and stable lesions; however, they may be unsightly or of cosmetic concern to patients. Rarely, the development of basal cell carcinoma within basaloid follicular hamartoma lesions has been reported. [17, 34, 32]

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