SAN DIEGO When it comes to evaluating basal cell carcinomas for Mohs surgery, experience trumps criteria, Dr. Ronald P. Rapini said at a meeting sponsored by the American Society for Mohs Surgery.
The more slides that physicians review, the better they are at distinguishing basal cell carcinoma (BCC) from other conditions, said Dr. Rapini, professor and chair of dermatology at the University of Texas, Houston, and the M.D. Anderson Cancer Center.
The main problem with BCC as it relates to Mohs surgery is that the cancer tends to resemble follicles, sweat ducts, and sebaceous glands in Mohs sections, he explained.
To best evaluate histopathology slides for basal cell carcinoma, the surgeon should scan images on low powerthe equivalent of flying over the tumor in a blimp and looking at it from a distanceand then zoom in for a closer look at anything that appears suspicious.
Get a special condenser for your microscope in order to have a 2x objective view, Dr. Rapini said. These condensers are more expensive but are worth it.
"You have to get in your blimp and look at the tumors from far away," he said. First find the tumor, then note the ink, then correlate it with the Mohs map of the problem area. "I prefer to look at the slide first and then look at the map. Even if the technician has flipped the sections by mistake, you can tell the orientation of the specimen from looking at the ink," Dr. Rapini said.
Looking for a BCC on a histopathology slide is sort of like finding a single black sheep in a herd of white sheep. "Look for bluish aggregates that don't look like they belong," he suggested.
Sometimes tumor cells will look like follicles, and sometimes they will clump together. When toluidine blue stain is used, purplish smudges of mucin are more apparent around tumors than around follicles, which can help distinguish between them.
"If you are unsure, scan on low power, and then get closer," Dr. Rapini said. Thick or fixed sections may have brownish areas that make tumor spotting more difficult, and these require a closer look with a higher-powered objective.
BCC often can be distinguished by looking for signs of an inflammatory reaction. Basaloid cells have the ability to differentiate toward sweat ducts, follicles, and sebaceous glands, but this rarely changes the prognosis.
The principal types of basal cell carcinoma are nodular, pigmented, superficial (also known as multicentric), and sclerosing (also known as morpheaform). The term "infiltrating BCC" is also used, but the definition depends on the user; the term has been used to describe any deeply invasive BCC and also has been used as a synonym for sclerosing or morpheaform BCC.
Micronodular BCC is a term currently in vogue in dermatology circles, even though its characteristics have been demonstrated in only one paper.
"It's supposed to be more aggressive than the average basal cell, but in my opinion, this definition is overrated," Dr. Rapini said. Any BCC can be aggressive or nonaggressive. Ordinary nodular BCC can get into bone, for instance, and sclerosing BCC can sometimes prove only a minor problem.
When the tumor does penetrate the bone, a multidisciplinary approach may be needed, including collaboration with a radiation therapist or orthopedist.
Folliculocentric basaloid proliferation is something else to consider in cases of potential BCC. Dr. Rapini cited the journal article that described funny-looking follicles (Arch. Dermatol. 1990;126:9006). "These follicles are benign, but they just look strange," Dr. Rapini said. "There may be some sort of phenomenon where the nearby basal cell stimulates the follicular infundibulum," he added.
It's critical to remember that evidence of follicular differentiation does not rule out the possibility of BCC, Dr. Rapini noted. However, if papillary mesenchymal bodies, hair bulbs, or hair shafts are present, the area is more likely to be benign than cancerous.
Dr. Rapini recommends deeper cuts and a higher-powered examination to look for things like necrosis and stromal retraction. "The presence of lymphocytes can help distinguish BCC from follicles, but that isn't always reliable, especially in patients with rosacea," he said.
Even when there is follicular differentiation, physicians should not rule out BCC in a patient with a solitary tumor, especially in sun-damaged skin. A benign trichoepithelioma, for instance, can be confused with BCC. With regard to these tumors, Dr. Rapini said, "when in doubt, cut it out."
Dr. Rapini pointed out that breast cancer is the most common tumor to metastasize in the skin, and it can look like a basal cell or sclerosing basal cell carcinoma. A breast cancer tumor usually sits in the dermis, however, without connecting to the surface, and the patient usually mentions a history of breast cancer. Most of these metastases occur on the chest, he said.