As a podiatrist, clinical awareness of sun damaged tissue is a vital portion of our dermatological assessment for it has been shown that the dorsum of the foot is one of the most neglected regions of the body when applying sunscreen. ²  Squamous cell carcinoma, basal cell carcinoma and malignant melanoma are all common cancers that can be found on the dorsum of the foot.  While basal cell carcinoma is the most common skin cancer for anatomical sites such as face and trunk, it is squamous cell carcinoma that is found to be most common in the feet.²

The following paragraphs will discuss the common pigmented lesions that can be seen in the lower extremity.

ACTINIC KERATOSIS

On exam, these present as reddish-brown macules or papules that are poorly circumscribed. They can be scaly and range from 2-5mm in diameter. They are considered pre-cancerous and can be considered an early form of squamous cell carcinoma.

Diagnosis: as with all lesions, if it is raised, perform a shave biopsy or 2-4mm punch for flat lesions.

In some cases, AK can sometimes resolve on their own only to return with sun exposure.⁵ In most cases however, the lesions are removed as a precaution. Some modalities for removal include cryosurgery, curettage and desiccation and laser surgery

Topical creams, gels and solutions are prescribed for use in patients with numerous or widespread actinic keratoses.

Approved medications

• 5-fluorouracil (Carac®,
• Efudex®,
• Fluoroplex®)
• Diclofenac (Solaraze®) and hyaluronic acid Imiquimod (Aldara®, Zyclara®)
• Tirbanibulin (Klisyri®)

BASAL CELL CARCINOMA

This is the most common form of skin cancer and accounts for more than .5 million cases diagnosed in the United States annually.  These can present as papules, plaques, nodules and pigmented lesions. These can also appear as a smooth papule with a central erosion or crust. BCC typically invades locally and rarely metastasizes.  Because they can growth in size, referral to dermatology is recommended for removal.

Some therapeutic interventions for more superficial basal cell carcinoma (BCC) include cryotherapy, topical chemotherapy, and photodynamic therapy.

More commonly, surgical intervention is utilized and this includes curettage, shave excision and standard excision. For larger and recurrent lesions, Mohs surgery will be employed.

SQUAMOUS CELL CARCINOMA

SCC typically arise from actinic keratosis as the result of exposure to UV radiation. Once actinic keratosis cells expand into the dermis they are then referred to as squamous cell carcinoma.

Squamous cell carcinoma most commonly appears as firm, smooth, or hyperkeratotic papule or plaque, often with central ulceration. Patients may describe a nonhealing lesion that bleeds with minimal trauma.

DIAGNOSIS

Shave biopsy if the lesion is raised, or 2-4mm punch if the lesion is flat

TREATMENT

Most SCC can be treated with curettage and electrodesiccation, cryotherapy, and excision. When recurrent, Mohs surgery is utilized.

Bowens disease (squamous carcinoma in situ) a more superficial version of SCC

Verrucous carcinoma is a more invasive, rare, variant of squamous cell carcinoma that commonly arises on the feet.  It is most common in the soles, but it can develop even on dorsal surface in areas of recurrent friction^. First-line treatment is complete surgical excision with wide margin; however, amputation may need to be performed due to local tissue destruction and late intervention.³

MALIGNANT MELANOMA

Melanoma accounts for only about 1% of skin cancers but causes a large majority of skin cancer deaths.⁴

The American Cancer Society’s estimates for melanoma in the United States for 2025 are:

• About 104,960 new melanomas will be diagnosed (about 60,550 in men and 44,410 in women).
• About 8,430 people are expected to die of melanoma (about 5,470 men and 2,960 women).⁴

Despite the statistics, melanoma is mostly curable if diagnosed and treated before reaching later stages. When diagnosing pigmented lesions, it is fundamental to be acquainted with “A,B,C,D” criteria for evaluation of pigmented lesions.

A (asymmetry)- lesions with irregular shapes and asymmetry are more unsettling. Whereas lesions that are round or oval are likely to be benign

B (border irregularity) irregularity to the border of the lesion is more concerning for malignancy while even and symmetrical borders tend to be benign

C (color) multiple shades of brown, black or blue black, red or white colorations are more troubling compared to less irregular pigmentation

D (diameter) Lesions greater than 6 mm warrant further evaluation, however earlier stages of melanoma may not precisely adhere to ABCD criteria.

Treatment

Surgical management is necessary and should likely be referred to a dermatologist.

Visual representations can be found by visiting The American Cancer Society.

Bibliography:

1. Gordon ML, Hecker MS. Care of the skin at midlife: Diagnosis of pigmented lesions. Geriatrics 1997; 52(Aug): 56-68

2. Jackson N, Allen T, Wagner R, Understanding Ultraviolet Radiation Dorsal Foot Injury at the Beach JAPMA Vol 109.No3. May/June 2019

3 D Nagarajan ¹, Malarvizhi Chandrasekhar ¹, Jim Jebakumar ¹, K Aravind Menon ^1,✉ Verrucous carcinoma of foot at an unusual site: Lessons to be learnt .Letter ,South Asian J Cancer

. 2017 Apr-Jun;6(2):63

4. Melanoma Skin Cancer | Understanding Melanoma. (n.d.). Www.cancer.org; American Cancer Society. https://www.cancer.org/cancer/types/melanoma-skin-cancer.html

5. Firnhaber J Diagnosis and Treatment of Basal Cell and Squamous Cell Carcinoma Am fam Physician. 2012;86(2):161-168

Todd Zeno, DPM is a podiatrist practicing in Hanover, Pennsylvania. He is a Past President of PPMA.