Identifying Skin Malignancies On The Distal Lower Extremity

Author(s): 
By James Q. Del Rosso, DO, FAOCD

Cutaneous malignancies and benign neoplasms simulating malignancy commonly affect the distal lower extremity, including the foot. One may see a variety of malignancy categories such as epithelial tumors, adnexal neoplasms, melanoytic neoplasms, vascular neoplasms and soft tissue tumors. Histologic confirmation of diagnosis is essentially mandatory, warranting the need to send all tissue specimens, including biopsy, incisional and excisional specimens, for pathology examination.
In some cases, the pathologist may incorporate immunohistochemical stains to differentiate specific tumor types. Developing and maintaining a close working relationship with a pathologist who is board-certified or highly skilled in dermatopathology is very helpful in optimizing clinical and histologic correlation in order to maximize diagnostic accuracy.
With this in mind, let’s take a closer look at three cases in which skin malignancy or clinical simulants affect the distal lower extremity.

Case One Presentation: A Firm, Slow-Growing Exophytic Nodule
A 46-year-old Caucasian male presented with a six-month history of a slowly growing, firm, well-defined, exophytic and asymptomatic nodule measuring 1.2 cm in diameter (see below photo). The lesion was on the proximal plantar surface. Approximately three months prior to presentation, the patient self-treated the lesion (which he thought was a wart) for two weeks with a topical salicylic acid 17% liquid. There was no response.

The major neoplasms in this differential diagnosis include pyogenic granuloma, amelanotic melanoma, squamous cell carcinoma and eccrine poroma.
In this case, obtaining an excisional biopsy is preferable. Unless you have a clinical suspicion of melanoma, you may also obtain a deep saucerization biopsy, which encompasses the breadth of the neoplasm and is respresentative of its deeper aspect. The histologic evaluation confirmed eccrine poroma.
Eccrine poroma is a benign tumor which arises from eccrine glands, which are sweat glands naturally found in high concentration on the palms and soles.1,2 This type of tumor may simulate other malignant or benign tumors as mentioned above in the differential diagnosis. Eccrine poromas are typically solitary. They are usually slightly pedunculated or surrounded by a keratotic collarette. You will often see them on the plantar or lateral surface of the foot and they are usually less than 2 cm in diameter.1,2
The treatment of eccrine poroma is surgical excision with clear pathologic margins in order to reduce the risk of recurrence. The presence of multiple small eccrine poroma papules on the palms and soles (eccrine poromatosis) is an unusual and very rare presentation.3 Although relatively uncommon, malignant eccrine poroma (porocarcinoma), arising within a long-standing eccrine poroma, may remain localized or may metastasize, usually forming multiple cutaneous metastases with possible associated visceral metastases.4,5
Due to the absence of melanotic pigment, amelanotic melanoma may look similar to eccrine poroma, as may a nodular form of squamous cell carcinoma.

Pyogenic granuloma, also referred to as lobular capillary hemangioma, is a benign proliferative angiomatous neoplasm, which tends to develop and grow rapidly over a period of a few weeks (see photo at right).6 The lesion may be pedunculated or associated with an epidermal collarette. Occurring anywhere on the cutaneous surface, including the feet, pyogenic granuloma usually has a red, vascular appearance and may be friable with easy bleeding.

Case Two Presentation: Large Erythematous Plaques
A 62-year-old female presented with two large, erythematous scaly asymptomatic plaques on the medial surface of her leg (see below photo at left). The lesions started smaller and slowly expanded in radial diameter over the course of at least eight years.
Previous treatment with a topical antifungal (econazole) cream for approximately one month produced no change. Subsequent treatment with a high potency topical corticosteroid for three weeks also produced no response. The patient did not have any other similar lesions and there was no regional adenopathy upon palpation.

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