PracticalDermatology

Abstract

We describe an 86-year-old male who presented with an erythematous nodule on his left forearm. Initial shave biopsy revealed a nodular basal cell carcinoma, and he was scheduled for definitive excision. Upon pathologic examination of the re-excised nodular basal cell, an incidental melanoma with Breslow Depth 1.1 mm was discovered. This case serves as a crucial reminder for Mohs surgeons, dermatologic surgeons, and dermatopathologists to be vigilant when examining pathologic specimens for other important diagnoses unrelated to the primary tumor being excised, to have a close working relationship with a local dermatopathologist, and to always consider skin cancer treatments that include pathologic evaluation, even for low-risk tumors.

Introduction

Incidental or collision tumors are not uncommon in cutaneous surgery and can represent either benign or malignant neoplasms. Based on previous reports, excised basal cell carcinomas (BCCs) most commonly include collisions with benign melanocytic nevi.¹ Conversely, the incidence of collision tumors involving a basal cell carcinoma and another keratinocyte carcinomas is often encountered, but extremely uncommon with more rare malignant neoplasms, such as cutaneous melanoma and merkel cell carcinoma. Incidental or collision lesions can sometimes be detected with visual inspection or dermoscopy, but other times are only apparent on pathologic evaluation by a dermatopathologist or Mohs surgeon. Such lesions may be subtle, thus diligent examination of the pathological margins is crucial to prevent oversight and thus, a missed diagnosis. In this case, we present a patient with an invasive melanoma that may otherwise have been missed if not for careful evaluation of all the tissue available to the pathologist.

Case Synopsis

An 86-year-old male patient presented to the clinic with a 1.5 x 1.5 cm erythematous, exophytic nodule on his left forearm [Figure 1]; dried serosanguinous crust from the biopsied basal cell is visible. No other lesions were visible in proximity to this nodule. The lesion was biopsied, and the pathology revealed a nodular BCC extending to both lateral margins and the deep margin. A standard excision was performed with 4 mm margins. A nodular basal cell corresponding to the clinically visible lesion was appreciated in pathologic evaluation. However, in only one section of the excised tissue, a melanoma with a Breslow depth of 1.1 mm, was noted at a lateral margin [Figures 2-4]. Figure 2 demonstrates the nodular basal cell carcinoma which was removed via the excision and was visible clinically. The presence of atypical melanocytes extending from the epidermis into the reticular dermis with enlarged irregular nuclei were noted and indicative of invasive melanoma [Figure 3, Figure 4]. Further evaluation of the lesion was performed with the PRAME immunostain, which aids in assessing margin clearance and is specific for malignant melanocytes.² As expected, the melanocytes were PRAME positive, reaffirming the diagnosis of margin-positive melanoma. The patient was treated with a wide local excision to the fascia by a surgical oncologist. The surgeon and patient opted out of a sentinel lymph node biopsy. Margins were clear after this procedure and the patient remains in remission after five months.

Figure 1. Visible exophytic plaque with generalized photoaging on the left forearm, no visible evidence of melanoma.

Figure 2. H&E stain showing nodular basal cell carcinoma from excised specimen.

Figure 3. H&E stain showing evidence of melanoma on the lateral margin of the excised specimen.

Figure 4. H&E stain showing melanoma extending to the reticular dermis.

Case Discussion

It is rare for basal cell carcinoma excision specimens to contain an incidental melanoma,³ especially in cases like the present, in which no melanocytic lesion was visible clinically. This patient’s invasive melanoma would not have been discovered unless the BCC was treated with a method which allowed for pathologic examination. There is an array of treatment options for BCC depending on factors such as tumor location, size, histologic features, health of the patient, and the patient’s preferences. Mohs micrographic surgery and standard surgical excision with pathologic margin evaluation are the only treatments that allow the examination of margins.⁴ While electrodessication and curettage, radiation, and cryotherapy may be suitable options for treating BCC in certain settings, these techniques do not allow for pathologic tissue evaluation and thus may result in missed secondary lesions, including those which may be more significant than the lesion that indicated excision, as in the present case. Each approach has benefits and drawbacks, however margin assessment with precise pathologic classification and histologic staging is ideal whenever possible. This lesion is on ill-defined skin and at 1.5 cm is considered moderate- not low-risk; excision would be the preferred treatment in this case. This case highlights the importance of complete tissue assessment to confirm the presence or absence of second primary tumors in a patient with significant actinic damage. For Mohs surgeons, this case underscores the importance of carefully inspecting all tissue on each slide and consulting with a dermatopathologist for additional staining and examination in cases where a collision tumor or other rare findings are suspected.

Conclusion

This case serves to remind cutaneous surgeons and dermatopathologists that tissue pathology may reveal the presence of other unexpected, yet significant tumors. Mohs surgeons and dermatopathologists alike should be diligent to review all tissue on every section and slide, and to be cognizant and alert for subtle or unexpected pathology unrelated to the neoplasm requiring treatment. Seemingly routine procedures always include the possibility of unusual or unexpected findings, demonstrating the importance of the broad education and training of board-certified dermatologists, Mohs surgeons, and dermatopathologists.

1. Boyd A, Rapini R. An analysis of 69 cases and review of the literature. Am J Dermatopathol. 1994;16(3):253-257.

2. Lezcano C, Jungbluth A, Nehal K, et al. PRAME expression in melanocytic tumors. Am J Surg Pathol. 2018 Nov; 42(11):1456-1465.

3. Papa G, Grandi G, Pascone M. Collision tumor of malignant skin cancers: A case of melanoma in basal cell carcinoma. Pathol Res Prac. September 11 2006;202(9):691-694. [PMID: 16876964]

4. Ducker A, Adam G, Rofeberg V, et al. Treatments of primary basal cell carcinoma of the skin. Ann Intern Med. 2018;169(7):456-466.