Basal cell carcinoma of the skin

by Allison Osmond, MD FRCPC
January 8, 2024

Basal cell carcinoma (BCC) is the most common type of skin cancer. It starts from basal cells normally found near the bottom of the epidermis, a thin layer of tissue on the surface of the skin. Most tumours occur in older adults on sun-exposed skin.

This article will help you understand your diagnosis and pathology report for basal cell carcinoma of the skin.

What causes basal cell carcinoma in the skin?

Prolonged and excessive exposure to UV radiation from the sun is the most common cause of basal cell carcinoma. Because they constantly divide, basal cells are more sensitive to DNA damage caused by long-term exposure to UV radiation from the sun.

Will the cells in basal cell carcinoma spread to other parts of the body?

The cancer cells in basal cell carcinoma rarely metastasize (spread) to lymph nodes or distant sites such as the lungs.

How is this diagnosis made?

The diagnosis is usually made after a small tissue sample is removed in a procedure called a biopsy. The diagnosis can also be made after the entire tumour is removed in a procedure called an excision. If the diagnosis is made after a biopsy, your doctor will probably recommend a second surgical procedure to remove the rest of the tumour.

Your pathology report for basal cell carcinoma

The information found in your pathology report for basal cell carcinoma plays an important role in your medical care. In addition to the diagnosis, most reports will include the subtype along with information about the tumour thickness, the presence or absence of perineural invasion and lymphovascular invasion, and the assessment of margins. These elements are described in greater detail in the sections below.

Types of basal cell carcinoma

Pathologists divide basal cell carcinoma into histologic types based on how the cancer cells stick together and the shapes they form as the tumour grows. The type can only be determined after the tumour has been examined under a microscope by a pathologist.  A tumour may be made up of one or multiple types of basal cell carcinoma.

Infiltrating type

Infiltrating is a high-risk type of basal cell carcinoma. It is called “infiltrating” because the tumour is made up of small groups of cancer cells that grow deeply into a part of the skin called the dermis. This deep pattern of invasion makes it difficult for surgeons to fully remove the tumour. As a result, this type is more likely to regrow after surgery compared to low-risk types of basal cell carcinoma.

Micronodular type

Micronodular is a high-risk type of basal cell carcinoma. This type of cancer is called “micronodular” because the tumour is made up of very small (“micro”) groups of cancer cells called nodules. The nodules of cancer cells typically spread deeply into a part of the skin called the dermis. This deep pattern of invasion makes it difficult for surgeons to fully remove the tumour. As a result, the micronodular type is more likely to regrow after surgery compared to low-risk types of basal cell carcinoma.

Nodular type

Nodular is the most common type of basal cell carcinoma. This type of cancer is called “nodular” because the tumour cells connect to form large groups called “nodules” in a layer of the skin called the dermis. It is considered a low-risk type of basal cell carcinoma.

Pigmented type

Pigmented is a low-risk type of basal cell carcinoma. This type of cancer is called “pigmented” because a pigment called melanin is found throughout the tumour. It is the melanin pigment that gives the tumour its dark colour.

Sclerosing type

Sclerosing (also called morphoeic) is a high-risk type of basal cell carcinoma. This type of cancer is called “sclerosing” because the tumour is made up of very small groups of cancer cells surrounded by dense connective tissue called collagen which pathologists describe as “sclerotic”. The groups of cancer cells typically spread deeply into a part of the skin called the dermis.  This deep pattern of invasion makes it difficult for surgeons to fully remove the tumour. As a result, the sclerosing type is more likely to regrow after surgery compared to low-risk types of basal cell carcinoma.

Superficial type

Superficial is a relatively common type of basal cell carcinoma. This type of cancer is called “superficial” because most of the tumour is found at the junction of the epidermis and the dermis, near the surface of the skin. It is considered a low-risk type of basal cell carcinoma.

Tumour thickness

Basal cell carcinoma of the skin starts in a thin layer of tissue on the surface of the skin called the epidermis. Tumour thickness is a measurement of how far the tumour cells have spread from the top of the epidermis into the layers of tissue below (the dermis and subcutaneous tissue). The tumour thickness is similar but different from the depth of invasion which is a measurement of how far the tumour cells have spread from the bottom of the epidermis to the deepest level of invasion.

Perineural invasion

Pathologists use the term “perineural invasion” to describe a situation where cancer cells attach to or invade a nerve. “Intraneural invasion” is a related term that specifically refers to cancer cells found inside a nerve. Nerves, resembling long wires, consist of groups of cells known as neurons. These nerves, present throughout the body, transmit information such as temperature, pressure, and pain between the body and the brain. Perineural invasion is important because it allows cancer cells to travel along the nerve into nearby organs and tissues, raising the risk of the tumour recurring after surgery.

Lymphovascular invasion

Lymphovascular invasion occurs when cancer cells invade a blood vessel or lymphatic channel. Blood vessels, thin tubes that carry blood throughout the body, contrast with lymphatic channels, which carry a fluid called lymph instead of blood. These lymphatic channels connect to small immune organs known as lymph nodes, scattered throughout the body. Lymphovascular invasion is important because it spreads cancer cells to other body parts, including lymph nodes or the lungs, via the blood or lymphatic vessels.

Margins

In pathology, a margin refers to the edge of tissue removed during tumour surgery. The margin status in a pathology report is important as it indicates whether the entire tumour was removed or if some was left behind. This information helps determine the need for further treatment.

Pathologists typically assess margins following a surgical procedure like an excision or resection, aimed at removing the entire tumour. Margins aren’t usually evaluated after a biopsy, which removes only part of the tumour. The number of margins reported and their size—how much normal tissue is between the tumour and the cut edge—vary based on the tissue type and tumour location.

Pathologists examine margins to check if tumour cells are present at the tissue’s cut edge. A positive margin, where tumour cells are found, suggests that some cancer may remain in the body. In contrast, a negative margin, with no tumour cells at the edge, suggests the tumour was fully removed. Some reports also measure the distance between the nearest tumour cells and the margin, even if all margins are negative. The micronodular and infiltrating types of basal cell carcinoma are associated with a higher risk of a positive margin because there is no clear boundary between the edge of the tumour and the adjacent normal tissue.

Completely excised

Completely excised means that the entire tumour was successfully removed by the surgical procedure performed. Pathologists determine if a tumour is completely excised by examining the margins of the tissue (see above for more information about margins).

Incompletely excised

Incompletely excised means that only part of the tumour was removed by the surgical procedure performed. Pathologists describe a tumour as being incompletely excised when tumour cells are seen at the margin or cut edge of the tissue (see above for more information about margins).

It is normal for a tumour to be incompletely excised after a small procedure such as a biopsy because these procedures are usually not performed to remove the entire tumour. However, larger procedures such as excisions and resections are usually performed to remove the entire tumour. If a tumour is incompletely excised, your doctor may recommend another procedure to remove the rest of the tumour.

Learn more about pathology

Atlas of pathology