Basal cell carcinoma (BCC) is the most common form of skin cancer. In general, these tumors are locally destructive, invading and destroying surrounding healthy skin and tissues, but rarely metastasizing and spreading into the body.
“These tumors are extremely common, and if left untended, can cause significant damage,” says Dr. Adam Mamelak, skin cancer specialist and fellowship trained Mohs micrographic surgeon in Austin, Texas. “But not all basal cell’s are the same. Different tumors can have different growth patterns and clinical behaviors. This makes some more amenable to certain treatments over others.”
Dr. Mamelak is referring to the different subtypes of basal cell carcinoma. While all are considered Basal Cell skin cancer, they can be classified by how they appear and grow on the skin, or what they look like under the microscope. These subtypes include:
Nodular: This type is encountered most frequently. It appears as a pink or flesh-colored bump, often with broken blood vessels coursing through or around the growth. It often has a pearl-like, shiny texture, and tends to be friable and bleed easily with the slightest manipulation. Although they can arise anywhere on the body, the face, head and neck tend to be the most common area these type of skin cancer appear. Under the microscope, large clusters or ‘nests’ of cancer cells are seen within skin’s dermal layers.
Micronodular: Unlike their nodular counterpart, much smaller clusters of malignant cells are observed under the microscope. This causes the appearance of this variant to be different on the skin. The numerous small nests also makes micronodular basal cells more deeply infiltrating into the skin, causing them to be more recalcitrant to treatment and prone to recurrence. They are less amenable to destructive treatments, such as curettage and electrodesiccation, and often better treated with therapies such as Mohs surgery.
Nodulocystic: Just as it sounds, these tumors are fluid filled and often have cavities. These cystic structures can be appreciated grossly on the skin with their blue-grey colored nodular appearance, or under the microscope with cavities within the nests of tumor.
Microcystic: These tumors often resemble milia – tiny white bumps that resemble keratin-filled cysts – on the skin.
Adenoid: Under the microscope, this subtype shows basal cell tumor cells forming gland-like structures in the skin. Their are thin strands of tumor cells with tubules and a few dilated cavities. The cyst-like cavities contain sugar-coated proteins called mucin.
Follicular: This variant of BCC possesses tumor cells that resemble hair follicles in the telogen phase of hair growth. Tiny infundibular cyst-like structures are observed under the microscope. The infundibulum is an anatomic term that refers to the upper portion of the hair follicle.
Infundibulocystic: This variant of BCC appears to have components of hair follicles admixed with tumor cells, when examined under the microscope. Specifically, infundibula and follicular germs, portions of the hair follicle, are observed within these tumors.
Pigmented: This subtype of basal cell carcinoma resembles the nodular variant, but with a brown or black color. The color is not thought to influence the behavior of the tumor (i.e. make it more or less aggressive).
Superficial: This is an extremely common variant of basal cell carcinoma. It often appears as a patch of discolored skin but may show broken blood vessels and a pearly texture (similar to the nodular subtype) on close inspection. These tumors are often mistaken for eczema or psoriasis as they grow. They are common on the trunk.
Infiltrative: This is an aggressive variant of basal cell carcinoma. Under the microscope, strands of tumor cells can be seen projecting into the dermal layer of the skin and coursing between collagen fibers. These variants are often treated with surgery as destructive treatments do not always effectively treat these tumors.
Morpheaform: Also known as sclerotic BCC, or cicatricial BCC, this subtypes often appears as a white, shiny, depressed scar-like growth on the skin. They most commonly appear on the on the head and neck. Infiltrating strands of tumor cells are again seen growing between collagen fibers in the skin’s dermis, the layer that lies just below the epidermis.
Rodent ulcer: This represents a clinical description of a BCC that has been left untreated for a long period of time. The center of the tumor can break down and an ulcer can form. The typical pearly texture or broken blood vessels can be concealed by the large eroded hole in the skin.
Neurotropic: The term neurotropic or neurotropism describes a tumor that affects the nerves or nervous system. This BCC variant can be more symptomatic than others, producing pain and discomfort, and can be difficult to surgically remove because of its microscopic extension along nerves in the skin.
Solitary basal cell carcinoma in young persons: Just as the name says, these BCC arise in younger individuals. They are not thought be occur from sun or excessive UV exposure; however, these malignancies arise at the site of developmental embryonic fusion clefts in the skin. This subtype is considered aggressive and can be quite invasive throughout the layers of the skin.
Basosquamous: Also known as metatypical BCC. Under the microscope, this subtype shows cellular features of both basal cell carcinoma and squamous cell carcinoma skin cancer. They are considered a more aggressive variant of BCC.
Pleomorphic: This variant of BCC has the addition of large atypical mononucleated and multinucleated giant tumor cells, with frequent and atypical mitoses observed when examined under the microscope. These tumors usually appear as growths on the head or neck.
Clear cell: Tumor cells can occasionally show clear cell changes when examined under the microscope. The clear cell appearance represents a degenerative change within the tumor cells themselves.
Granular cell: This is another term used to describe the appearance of the individual tumor cells. Under the microscope, the cells contain small pink granules that may also represent a degenerative change.
Singlet ring cell: This term is rarely used to describe BCC. Close inspection of individual tumor cells under them microscope reveals that the cells’ nuclei become compressed by the accumulation of other cellular materials, creating a ‘singlet ring’ appearance.
“Some of these classifications are certainly more academic than carry any real clinical significance,” explains Dr. Mamelak. “By far, the most common subtypes we see are nodular, superficial, infiltrative, nodulocystic, morpheaform and pigmented. But it is important to know about these other subtypes, especially when examining tissue under the microscrope during Mohs surgery.
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If you have been diagnosed with Basal Cell Carincoma, or have questions about skin cancer treatment, please contact us at Sanova Dermatology and the Austin Mohs Surgery Center today.
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