Basal cell carcinoma (BCC) is the most common cutaneous tumor, comprising around 70% of all skin malignancies. It may sometimes display overlapping histopathologic findings with benign follicular tumors such as trichoepithelioma (TE), which is a rare non-malignant tumor of hair follicles.
We present a case of pigmented BCC that was clinically and dermoscopically recognized, but had histopathological features favoring TE in the first biopsy, which was followed by an excision biopsy that revealed a diagnosis of adenoid BCC, a rare histological variant of BCC.
A 66-year-old female, homemaker by occupation presented to the dermatology outpatient department with a two and a half years history of a spontaneously occurring dark colored raised lesion on her right cheek. There was no history of excessive sun exposure. The lesion started as a coin sized mole which after an accidental nail trauma, bled and started to gradually increase in size since past 7 months. The lesion was occasionally itchy and painless.
Before coming to our hospital, she sought ayurvedic treatment which comprised of topical cream application but without any relief. She had hypertension, well controlled on Telmisartan. There was no history of radiation exposure and no past history or family history of skin cancers.
On examination, she had a well circumscribed indurated, non-tender hyperpigmented plaque with an elevated border measuring 5 cm × 3 cm on the right infraorbital region with central ulceration [Figure 1]. There was no regional lymphadenopathy.
Dermoscopy (DL4 3rd gen, 10× polarized contact mode) revealed arborizing vessels, blue grey dots, globules, and milia-like cysts, as well as multiple aggregated whitish-yellow (MAY) globules with a deeply pigmented border and flecks of brown pigment [Figure 2], pointing to a provisional diagnosis of pigmented BCC.
A punch biopsy for histopathology showed unremarkable epidermis. Nests of uniform basaloid cells with peripheral palisading and branching without any connection to the overlying epidermis were seen in the loosely arranged stroma of the dermis. Abortive hair follicle differentiation, foci of melanin pigmentation and horn cysts were also noted in the cell nests, Figure 3 favoring a diagnosis of TE. For further confirmation, immunohistochemistry (IHC) was performed which showed diffuse positivity of Bcl-2 and focal positivity of CD 10 in peritumoral stroma along with strong staining of CD 34 favoring BCC and TE respectively [Figure 4A–C].
Due to the diagnostic ambiguity and a strong clinical suspicion of BCC, an excision biopsy was performed. The excision biopsy revealed features of Adenoid BCC, showing basaloid tumor cells connected to epidermis and arranged in nests and glands in a loose, mucinous matrix, extending into deep dermis [Figure 5A and B]. All resected margins were free of tumor.
There has been no recurrence on 2 monthly follow ups.
While TE usually occurs as a skin-colored nodule or a papule on the head and neck, BCC presents as a pearly white to translucent lesion with raised peripheral margins with or without pigmentation and ulceration.
Common dermoscopic features defined for BCC include spoke-wheel areas, leaf-like areas, large blue-grey ovoid nests, multiple blue-grey globules, arborizing vessels, annular distribution of telangiectatic vessels, and multiple erosions/ulcerations. Pigmented BCC usually has flecks of pigment with an absence of pigmented network. Presence of MAY globules is a recent finding reported in a study by Vinay et al. Tumors such as desmoplastic TE may show some overlap with arborizing telangiectasia, ivory (or pearl) white background, and keratin cysts.
In our case, the dermoscopic findings were consistent with a pigmented BCC with ulceration
Histologically, both TE and BCC exhibit nests of basaloid cells with follicular differentiation.
However, TE, a benign neoplasm of the hair follicles can be differentiated based on the presence of papillary mesenchymal bodies or abortive hair follicle differentiation and fibrous stroma.
BCC on the other hand is a malignant tumor composed of hyperchromatic basaloid cell nests originating from basal cell layer of the epidermis or outer root sheath of hair follicles. Frequent mitosis, necrotic tumor cells, tumor-stroma cleft formation, keratinous cysts, ulceration, inflammatory response, stromal edema, and peri-tumoral mucin production are other features.
These histopathological features as well as the protein expression on immunohistochemistry may overlap, making differentiation difficult for the pathologist.
On IHC, bcl 2 expression is confined to the peripheral basaloid cells in TE, in contrast to the diffuse positivity in BCC. Stromal cells of TE express CD34, in contrast to BCC stroma. Several authors, however, have questioned the accuracy of using bcl-2 and CD34 expression to distinguish between the two.
CD10 expression by the peritumoral stroma alone favors a diagnosis of TE, whereas basaloid cell staining indicates a diagnosis of BCC.
Our patient had a diffuse reactivity with bcl 2 and focal positivity of CD 10 which supported the diagnosis of BCC but CD 34 positivity favored TE, adding to the confusion.
Cytokeratin profiling of BCC displays CK5/6 and CK14 expression and absence of CK20. Ber-EP4 typically shows strong expression. TE shows CK20 and PHLDA1 expression.
Table 1 summarizes the important differences between BCC and TE on IHC.
Due to paucity of IHC markers at our center these special stains could not be performed.
Adenoid BCC is an uncommon histopathological variant with a reported frequency of 1.3%.
It is often regarded as a low-grade malignancy compared to other high-grade subtypes like nodular and morpheaform.
It may be distinct in that it prefers less-exposed areas such as the back and axilla, and the lesions are larger. Histopathology shows tubular differentiation with small uniform cells with peripheral palisading, arranged in nests and cords with intertwining strands in a lace-like pattern.
The initial biopsy of our patient revealed signs of TE, which may have been inadequate to confirm the diagnosis, as demonstrated by features of adenoid BCC on the excision biopsy. Repeat IHC profiling was deemed unnecessary.
BCC can occasionally imitate TE more so histologically than clinically, which can be harmful because it might offer the patient and doctor a false sense of confidence, leading to undertreatment.
As a result, despite contradicting histologic results, one must prioritize a high clinical index of suspicion and strengthen it with dermoscopic findings, as well as order repeat biopsies for thorough confirmation to avoid missing rarer variants.
Our case highlights the diagnostic conundrum between TE and BCC, as well as the reporting of an uncommon form, Adenoid BCC, which has limited literature on its clinical profile.
I would like to sincerely thank Dr Charanjeet Ahluwalia (Professor, Department of Pathology, VMMC)for the final reporting of the case and Dr Aman Kumar (Senior Resident, Department of Pathology, VMMC) who provided with the histology pictures. Criteria for inclusion in the authors’/ contributors’ list—The case was assessed by Dr. Prateek and written predominantly by Dr. Prateek with inputs by Dr. V. Ramesh, Dr. Shruti, and Dr. Ahluwalia. Dr. Shruti was instrumental in guiding about the nature of the sequential biopsies. The manuscript has been read and approved by all the authors and the requirements for authorship as stated earlier in this document have been met, and that each author believes that the manuscript represents honest work, if that information is not provided in another form.
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