RCOphth Annual Congress 2026

A rare case of Porocarcinoma at the lateral canthus as a mimic of basal cell carcinoma

Introduction - Porocarcinoma

•Rare malignant tumour of the eccrine sweat glands

•Most commonly affects the upper and lower limbs, trunk, head and neck

•Eyelid involvement is exceptionally rare.

•Can arise de novo or from malignant transformation of a pre-existing benign lesion

•Clinically significant due to:

•Risk of local recurrence

•Regional lymph node involvement

•Potential for distant metastases (lung and bone)

Case history

A woman in her 90s seen in the oculoplastic clinic following referral from the dermatology department.

Presentation:

•Slowly growing crusting lesion at the left lateral canthus (Present for 18 months).

•Telangiectasia noted at the base, suspicious of a basal cell carcinoma (BCC)

Histopathology (Excision biopsy):

•Focus of residual poroma, additional focus of squamous differentiation

•Strongly positive for EMA and BerEP4.

•Consistent with malignant adnexal tumour, favouring Porocarcinoma

Management and outcome:

•Complete excision with clear 2mm margin

•No recurrence at 8-week post-operative review

H&E stained Porocarcinoma sections:

-Fig. 1: Low power (2x) view with arrows indicating sharp demarcation from the adjacent epithelium.

-Fig. 2: High power (10x) view showing infiltrative nature.

-Fig. 3: Adjacent benign poroma (black arrow) with invasive component (blue arrow).

Special stains of the Porocarcinoma for subsequent analysis:

-Fig. 4: BerEP4 stain at 1x magnification, staining strongly and diffusely.

-Fig. 5: EMA stain at 1x magnification, staining strongly and diffusely.

-Fig. 6: EMA stain at 20x magnification, highlighting ductal structures (black arrow).

Diagnosis

Commonly misdiagnosed as

•Poroma

•Basal cell carcinoma

•Squamous cell carcinoma

•Sebaceous carcinoma

Poor prognostic features

•Large tumour size

•Ulceration

•Rapid tumour growth

•Head and neck location

Preferred method of treatment:

•Wide local excision or mohs micrographic surgery to ensure clear margins

•Chemotherapy if evidence of multiple lymph nodes or distant metastases

Histopathology

•EMA and CEA show ductal luminal borders

•CD117, CK19 and BerEP4 indicate Porocarcinoma over SCC

Regular follow-up encouraged due to recurrence risk

Conclusion

•Early identification and histopathology diagnosis is paramount and will help prevent recurrence

•BerEP4 along with strong EMA staining and ductal differentiation strongly suggests Porocarcinoma over basal cell carcinoma (over strong BerEP4 alone).

•Regular monitoring of scar site and local lymph nodes help early recognition of recurrence/metastases

References:

References

1.Kurisu, Y., Tsuji, M., Yasuda, E., & Shibayama, Y. (2013). A case of eccrine porocarcinoma: usefulness of immunostain for s-100 protein in the diagnoses of recurrent and metastatic dedifferentiated lesions. Annals of dermatology, 25(3), 348–351. https://doi.org/10.5021/ad.2013.25.3.348

2.Goto, K., Ishikawa, M., Hamada, K., Muramatsu, K., Naka, M., Honma, K., & Sugino, T. (2021). Comparison of Immunohistochemical Expression of Cytokeratin 19, c-KIT, BerEP4, GATA3, and NUTM1 Between Porocarcinoma and Squamous Cell Carcinoma. The American Journal of dermatopathology, 43(11), 781–787. https://doi.org/10.1097/DAD.0000000000001901

RCOphth Annual Congress 2026

A rare case of porocarcinoma located at the lateral canthus as a mimic of basal cell carcinoma

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