DISCUSSION
Prior to consulting dermatology, this patient had talked extensively with his primary care provider (PCP) about the large lesion on his back. The PCP was quite sure the cause was a fungal organism and assured the patient that the prescribed antifungal cream would almost certainly cure it. This is a scenario in which almost every PCP will participate at some point early in his/her career. When treatment fails, the patient is then referred to dermatology—where a totally unexpected diagnosis is made.
This case represents the natural history of superficial basal cell carcinoma (SBCC), the appearance of which is at odds with any other kind of skin cancer, including the other types of basal cell carcinoma. SBCC is especially common on the shoulders and trunks of patients with a history of excessive sun exposure. The mid-back location on this patient is quite typical, as is the annular, scaly morphology.
The cancer—which originates in a row of cells at the base of the epidermis—effectively destroys surface structures such as skin lines and hair follicles as it spreads laterally. Left in place long enough, SBCCs can eventually become focally invasive and can even spread into regional lymph nodes. Metastasis from them is extremely rare but has been reported.
Treatment is therefore necessary and can range from surgical excision of smaller lesions to electrodessication and curettage to nonsurgical options, such as the application of imiquimod creams or 5-fluorouracil cream, or even radiation therapy. This man was treated with thrice-weekly application of imiquimod 3.75% cream for at least two months, which will cause irritation and scant drainage but will likely result in a cure.
One of the main benefits of his presentation to dermatology was the opportunity to encourage and facilitate yearly skin check-ups—important, given his risk for other sun-caused skin cancers (especially melanoma).
A major learning point to be gained from this case: Just because a lesion is annular and scaly doesn’t mean it’s fungal. The fungi have to have a source (animal, child, soil), and it helps a lot if the affected area is damp and warm (eg, groin or under a bulletproof vest). Immunosuppression (from corticosteroid use, especially) helps as well.
Besides fungal infection, the differential for this type of lesion includes Bowen’s disease (intraepidermal squamous cell carcinoma), psoriasis, and eczema. The fact that the lesion was fixed (did not come and go), grew steadily, and was on the directly sun-exposed skin of a person with a history of heavy sun exposure all pointed to the diagnosis.
TAKE-HOME LEARNING POINTS
• Superficial BCC (SBCC) has also been called “field fire” skin cancer because of the prominent, well-defined scaly border that expands peripherally and leaves a “scorched earth” look behind.
• SBCCs are common on skin directly exposed to the sun, especially backs and arms.
• SBCCs do not resemble other types of BCC at all and are therefore often mistaken for “fungal infection.”
• Pay as much attention to the patient as to the lesion. There was abundant evidence of excessive sun damage on this patient’s trunk, making him an ideal patient for skin cancer.