Basaloid Follicular Hamartoma Workup

Updated: Aug 09, 2022
  • Author: Kara Melissa Torres Culala, MD; Chief Editor: Dirk M Elston, MD  more...
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Laboratory Studies

No specific tests are required to establish a diagnosis of basaloid follicular hamartoma (BFH) other than skin biopsy. However, given the association between multiple basaloid follicular hamartoma and autoimmune diseases such as systemic lupus erythematosus (SLE) and myasthenia gravis, a comprehensive history and physical examination should be performed. If the clinical index of suspicion for autoimmune disease is strong, the following laboratory tests may be ordered:

  • Antinuclear antibody testing

  • Double-stranded (ds) DNA antibody testing

  • Ro (ssA) and La (ssB) antibody testing

  • CBC count with differential

  • Urinalysis

  • Chemistry panel

  • Complement levels

  • Antiacetylcholine antibody testing

Patients may present clinically with nevoid basal cell carcinoma syndrome (NBCCS) with overlapping features of basaloid follicular hamartoma. To avoid excessive surgical treatment should the lesion be a benign basaloid follicular hamartoma, the identification of a de novo mutation of c.1291delC in the PTCH1 gene helps to confirm the diagnosis of nevoid basal cell carcinoma syndrome. [55]


Imaging Studies

Imaging studies may be useful to distinguish patients with multiple basaloid follicular hamartoma (BFH) from those with nevoid basal cell carcinoma syndrome (NBCCS). Specifically, nevoid basal cell carcinoma syndrome patients may display odontogenic jaw keratocysts, intracranial calcification (eg, of the falx cerebri), and rib anomalies. The following specific studies may be obtained to identify patients suggested of having nevoid basal cell carcinoma syndrome:

  • Panorex films of the jaw

  • Skull radiography

  • Chest radiography


Histologic Findings

The definitive diagnosis of basaloid follicular hamartoma (BFH) is based on histologic findings. Despite the wide range of clinical manifestations, the histologic features of basaloid follicular hamartoma are relatively consistent for all its forms. [56, 57, 58] See the image below.

Basaloid follicular hamartoma. Courtesy of L Wozni Basaloid follicular hamartoma. Courtesy of L Wozniak & KW Zielinski (own work), via Wikimedia Commons.

Anastomosing thick cords and thin strands of basaloid cells are localized to the superficial dermis. [18, 59] In contrast, infundibulocystic basal cell carcinoma (BCC) may involve the subcutaneous fat and skeletal muscle. [59]

Lesions of basaloid follicular hamartoma are unattached to the epidermis and extend from the infundibular portion of vellus hair follicles. [20]

Mitoses and single cell necrosis are generally few, if at all present, in basaloid follicular hamartoma. [20, 40, 60] A prominence of these findings is more consistent with basal cell carcinoma. [20, 40]

The stroma in basaloid follicular hamartoma is mildly cellular and fibromyxoid. [18, 40] The peritumoral stroma was found to have positive CD34 and CD10 staining. [52, 60, 61]

Specific immunostaining studies may help to distinguish basaloid follicular hamartoma from basal cell carcinoma. Basaloid follicular hamartoma has a lower cell proliferative index of the proliferative cell nuclear antigen (PCNA) and Ki-67 compared with basal cell carcinoma. [20, 60] Basaloid follicular hamartoma also has positive immunoreactivity to CK20 and plectin homology–like domain, family A, and member 1 protein (PHLDA1) that is typically negative in basal cell carcinoma. [1]  Although, Hazemann et al found PHLDA1 to be weakly expressed in BFH lesions. [62] Bcl-2 is positive only within the outermost cells bordering the stroma in basaloid follicular hamartoma, in contrast to a significant bcl-2 expression found in the more aggressive forms of basal cell carcinoma. [52, 61, 63, 64] Other positive stains that may be seen in basaloid follicular hamartoma are S100 in the epithelial nests and stroma and factor VIIIa in the dendritic cells adjacent to the epithelial nests. [33]