Basal Cell Carcinoma of the Skin: : Understanding Your Pathology Report

by Allison Osmond, MD FRCPC
April 23, 2026

Basal cell carcinoma (BCC) is the most common type of skin cancer. It starts from basal cells, which are found in the deepest layer of the epidermis (the outer layer of the skin) and in hair follicles. Under the microscope, all basal cell carcinomas are made up of clusters of small, darkly stained cells called basaloid cells.

Basal cell carcinomas grow slowly and almost never spread to other parts of the body. However, if left untreated, they can grow larger and damage nearby tissues, particularly on the face near the eyes, ears, or nose. Pathologists divide basal cell carcinoma into several types based on how the cancer cells arrange themselves under the microscope. Some types behave more aggressively than others and are more likely to come back after surgery.

This article will help you understand the findings in your pathology report for basal cell carcinoma of the skin — what each term means and why it matters for your care.

What causes basal cell carcinoma?

The main cause of basal cell carcinoma is long-term damage to the DNA in skin cells from ultraviolet (UV) radiation. Most of this damage comes from sunlight, but artificial sources such as tanning beds can cause similar damage. For basal cell carcinoma, intense intermittent sun exposure — such as severe sunburns, especially during childhood — appears to be particularly important. This is different from squamous cell carcinoma of the skin, which is more closely linked to the total amount of UV exposure accumulated over a lifetime.

Other risk factors include:

• Fair skin — People with lighter skin, light-colored eyes, and red or blond hair are at higher risk because their skin contains less protective melanin.
• Older age and male sex — Most basal cell carcinomas occur after age 50, and men are more commonly affected than women.
• Previous radiation therapy — Skin that received radiation in the past, particularly during childhood, has an increased risk of developing basal cell carcinoma years later.
• Weakened immune system — People taking anti-rejection medications after an organ transplant or living with other forms of immune suppression have a higher risk.
• Chronic arsenic exposure — Long-term exposure to arsenic, sometimes through contaminated drinking water, is associated with basal cell carcinoma.
• Genetic conditions — Inherited conditions such as Gorlin syndrome (also called nevoid basal cell carcinoma syndrome), xeroderma pigmentosum, Bazex-Dupré-Christol syndrome, and Rombo syndrome greatly increase the risk, often leading to multiple basal cell carcinomas at a young age.
• Inherited pigmentation genes — Variations in genes such as MC1R, ASIP, and TYR, which help control skin and hair color, can also increase risk.

What are the symptoms of basal cell carcinoma?

Basal cell carcinoma often appears as a small, painless bump or patch that slowly grows over time. The appearance can vary depending on the type, but may include:

• A shiny or pearly bump, often with small visible blood vessels on the surface.
• A flat, scaly, or reddish patch.
• A sore that heals and then reopens, sometimes bleeding or crusting.
• A white, waxy, or scar-like area without a clear cause.

Basal cell carcinomas are most commonly found on areas of the skin that receive frequent sun exposure, such as the face, neck, ears, scalp, and arms. Any persistent change in the skin should be checked by a healthcare professional.

How is the diagnosis made?

The diagnosis of basal cell carcinoma is made after a tissue sample is examined under the microscope by a pathologist. The sample is obtained by a skin biopsy. Depending on the size and location of the lesion, the biopsy may be a shave biopsy (the surface of the lesion is shaved off), a punch biopsy (a small cylinder of skin is removed with a circular tool), or an excisional biopsy (the entire lesion is removed). Under the microscope, the pathologist looks for nests or clusters of basaloid cells that have grown down from the epidermis into the deeper layers of the skin. These cells are usually arranged with the outermost cells lined up neatly in a row — a feature called peripheral palisading — and there is often a clear space separating the tumor from the surrounding tissue. Imaging is rarely needed for basal cell carcinoma because the cancer very seldom spreads, but it may be considered for large tumors, tumors in difficult locations, or tumors suspected of invading deeper structures such as bone.

Types of basal cell carcinoma

Pathologists divide basal cell carcinoma into several types based on how the cancer cells arrange themselves under the microscope. The type matters because some patterns are more likely than others to grow deeply into the skin and come back after surgery. It is common for a single tumor to show more than one type, and the report may describe the most aggressive pattern present.

Low-risk types

• Nodular — The most common type of basal cell carcinoma. The cancer cells form large, well-defined clusters (nodules) in the dermis. Nodular basal cell carcinoma usually has a clear border, which makes it easier to remove completely with surgery.
• Superficial — The cancer cells are found at the junction between the epidermis and the dermis, near the surface of the skin, and do not grow deeply. This type often appears as a flat, scaly red patch.
• Pigmented — A variant in which the tumor contains the pigment melanin, giving it a dark brown or black color. Pigmented basal cell carcinoma can resemble melanoma and is usually a pigmented form of nodular or superficial BCC. It is not more aggressive than other low-risk types.
• Fibroepithelioma of Pinkus — An uncommon low-risk variant that often appears on the lower back as a pink, skin-tag-like growth. Under the microscope, thin strands of basaloid cells are embedded in loose connective tissue.

High-risk types

• Infiltrating — The cancer cells form small, irregular groups that spread deeply into the dermis. Because the edge of the tumor is poorly defined, it is more difficult to remove completely, and infiltrating basal cell carcinoma is more likely to come back after surgery than low-risk types.
• Micronodular — The cancer forms very small clusters of cells that spread deeply into the dermis. As with the infiltrating type, the indistinct edge makes complete removal challenging and increases the risk of recurrence.
• Sclerosing (morpheaform) — The cancer cells form thin strands surrounded by dense, scar-like connective tissue. This type often looks like a white, waxy scar on the skin and has an indistinct edge, both clinically and under the microscope, making it difficult to remove completely.
• Basosquamous (metatypical) — A variant that shows features of both basal cell carcinoma and squamous cell carcinoma. Basosquamous carcinoma behaves more aggressively than typical basal cell carcinoma and carries a small but real risk of spreading to lymph nodes or distant organs.

Tumor thickness and depth of invasion

Some pathology reports include measurements of tumor thickness or depth of invasion. Tumor thickness measures the distance from the skin surface to the deepest part of the tumor, while depth of invasion measures how far the cancer cells have grown from the bottom of the epidermis into deeper tissue below. Deeper tumors — particularly those that reach into the subcutaneous fat or beyond — are more difficult to remove completely and are more likely to come back after surgery.

Perineural invasion

Perineural invasion (PNI) means cancer cells are growing along or into a nerve. Nerves travel through the body like long wires, carrying signals such as temperature, pressure, and pain. Perineural invasion is an important finding because nerves can serve as highways that allow cancer cells to spread beyond the visible edge of the tumor. Perineural invasion makes the cancer harder to remove completely and is associated with a higher risk of the tumor coming back. When perineural invasion is present, particularly when a large, named nerve is involved, additional surgery or radiation therapy may be recommended.

Lymphovascular invasion

Lymphovascular invasion (LVI) means cancer cells have entered a small blood vessel or lymphatic channel. Blood vessels and lymphatic channels provide a route for cancer cells to spread to lymph nodes or distant organs. Lymphovascular invasion is very rare in basal cell carcinoma and, when seen, typically occurs in high-risk types or in tumors that have been present for a long time.

Margins

A margin is the edge of the tissue removed during surgery. Pathologists examine margins under the microscope to see whether any cancer cells are present at the cut edge. For basal cell carcinoma, both the peripheral margin (the sides of the removed skin) and the deep margin (the base of the removed tissue) are evaluated.

• Negative margin — No cancer cells are seen at the cut edge. The tumor is considered completely excised, and the risk of recurrence is low.
• Close margin — Cancer cells are within a short distance of the cut edge but do not reach it. Close margins are associated with a somewhat higher risk of recurrence, particularly with high-risk types.
• Positive margin — Cancer cells are present at the cut edge. The tumor is considered incompletely excised, meaning some cancer may have been left behind. Additional treatment — often a second surgery — is usually recommended.

The infiltrating, micronodular, and sclerosing types of basal cell carcinoma are more likely to have positive margins because they lack a clear boundary between the tumor and the surrounding normal tissue.

Lymph nodes

Basal cell carcinoma almost never spreads to lymph nodes, and lymph nodes are not usually removed or examined as part of treatment. Spread to lymph nodes occurs in far less than 1% of cases overall and is most often seen with long-neglected, very large, or aggressive types such as basosquamous carcinoma. If lymph nodes are removed and contain cancer cells, the report will describe the number of nodes examined, the number that contain cancer, and whether extranodal extension is present — meaning cancer cells have broken through the outer capsule of a lymph node into surrounding tissue.

Biomarker and molecular testing

Routine biomarker testing is not performed for basal cell carcinoma that can be managed with surgery alone. However, molecular information becomes important for two specific situations: locally advanced or metastatic disease that cannot be cured by surgery or radiation, and suspected inherited syndromes such as Gorlin syndrome.

The Hedgehog pathway

Nearly all basal cell carcinomas are driven by abnormal activity of a signaling system called the Hedgehog pathway. In most tumors, this is caused by a mutation that inactivates a gene called PTCH1, or, less often, by a mutation that activates a gene called SMO. Either change leaves the Hedgehog pathway permanently activated, which drives basaloid cells to proliferate and form a tumor.

This discovery led to the development of targeted drugs called Hedgehog pathway inhibitors. The drugs vismodegib (Erivedge) and sonidegib (Odomzo) block the SMO protein and shut down the pathway. Both are approved for locally advanced basal cell carcinoma that cannot be cured by surgery or radiation, and vismodegib is also approved for metastatic basal cell carcinoma. Routine testing for PTCH1 or SMO mutations is not required before starting these drugs, because the Hedgehog pathway is active in almost all basal cell carcinomas.

Immunotherapy

For basal cell carcinoma that has progressed on or cannot tolerate Hedgehog inhibitors, the PD-1 inhibitor cemiplimab (Libtayo) is approved. Cemiplimab is a type of immunotherapy that helps the immune system recognize and attack cancer cells. PD-L1 testing is not required before starting cemiplimab for basal cell carcinoma.

Gorlin syndrome and other inherited causes

Most basal cell carcinomas develop because of UV-related DNA damage and are not inherited. However, a small number of patients have an inherited condition called Gorlin syndrome (also known as nevoid basal cell carcinoma syndrome), caused by a germline mutation in the PTCH1 gene. People with Gorlin syndrome typically develop many basal cell carcinomas at a young age and may also have other findings, such as jaw cysts, pits on the palms of the hands, and specific skeletal abnormalities. If Gorlin syndrome is suspected — for example, in a patient who has multiple basal cell carcinomas before age 30, or a strong family history — genetic counseling and germline testing are recommended.

For more information about biomarkers and molecular testing in cancer, visit the Biomarkers and Genetic Testing section.

Is basal cell carcinoma staged?

Unlike most cancers, basal cell carcinoma is generally not assigned a pathologic stage. The American Joint Committee on Cancer (AJCC) does not include basal cell carcinoma in its TNM staging system because the cancer so rarely spreads to lymph nodes or distant organs. Instead, the risk of recurrence and spread is estimated from individual tumor features — such as size, location, histologic type, depth of invasion, perineural invasion, and margin status. In the uncommon situation where a basal cell carcinoma has spread locally into bone or to lymph nodes or distant organs, the same TNM criteria used for cutaneous squamous cell carcinoma may be applied.

What is the prognosis?

The prognosis for basal cell carcinoma is excellent. These tumors grow slowly and, in the vast majority of cases, are cured by a single surgical procedure. The five-year cure rate for primary, low-risk basal cell carcinoma treated with appropriate surgery is greater than 95%.

Features that increase the risk of local recurrence or, very rarely, spread include:

• High-risk histologic type — Infiltrating, micronodular, sclerosing, and basosquamous types are more likely to recur after surgery than the nodular or superficial types.
• High-risk location — Tumors on the central face, around the eyes, ears, and nose (the so-called “H-zone”) are more prone to recurrence and can be more difficult to remove while preserving function and appearance.
• Large tumor size — Larger tumors are more difficult to remove completely.
• Deep invasion — Tumors that invade into the subcutaneous fat or deeper structures carry a higher risk of recurrence.
• Perineural invasion — Particularly when a large, named nerve is involved.
• Positive or close surgical margins — Indicate that some tumor may have been left behind and increase the risk of recurrence.
• Recurrent tumor — A basal cell carcinoma that has come back after previous treatment is more difficult to cure than a new tumor.
• Immunosuppression — People on long-term immunosuppressant medications, including organ transplant recipients, are more likely to have multiple basal cell carcinomas and may experience more aggressive behavior.

Having one basal cell carcinoma increases the risk of developing additional basal cell carcinomas and other skin cancers in the future, which is why ongoing skin examinations and sun protection remain important after treatment.

What happens after the diagnosis?

Treatment of basal cell carcinoma is usually coordinated by a dermatologist and, in some cases, a surgeon (often a Mohs surgeon for high-risk or cosmetically sensitive areas). Most basal cell carcinomas are treated with surgery.

For small, low-risk tumors, options include standard surgical excision with a margin of healthy tissue, electrodesiccation and curettage (scraping and burning), cryotherapy (freezing), or topical medications such as imiquimod or 5-fluorouracil. For larger, high-risk, or recurrent tumors — and for tumors on the face where tissue preservation is important — Mohs micrographic surgery is often preferred. In this technique, the tumor is removed in thin layers that are examined under the microscope during the operation to confirm that all cancer cells have been removed.

Radiation therapy may be recommended after surgery when there are high-risk features such as perineural invasion of a named nerve or positive margins that cannot be re-excised. Radiation can also be used as the primary treatment for patients who are not candidates for surgery.

For the small number of patients with locally advanced or metastatic basal cell carcinoma that cannot be controlled by surgery or radiation, systemic therapy with a Hedgehog pathway inhibitor (vismodegib or sonidegib) is usually the first option, followed by the PD-1 inhibitor cemiplimab if the cancer progresses on or cannot tolerate Hedgehog inhibitors.

After treatment, regular skin examinations are important. People who have had one basal cell carcinoma are at higher risk of developing additional skin cancers, and consistent sun protection is a key part of prevention.

Questions to ask your doctor

• Where on my body did the basal cell carcinoma develop, and how large was the tumor?
• What type of basal cell carcinoma did I have? Is it considered low-risk or high-risk?
• Did the tumor show more than one histologic type?
• How deep did the tumor grow?
• Was perineural invasion found? If so, was a large, named nerve involved?
• Were the surgical margins negative, close, or positive? Do I need further surgery?
• What is my risk of the cancer coming back in the same area?
• Do I need any additional treatment, such as radiation therapy?
• How often should I have skin checks, and by whom?
• What steps can I take to reduce my risk of developing new skin cancers?
• Given my age, family history, and number of basal cell carcinomas, should I be evaluated for Gorlin syndrome or another inherited condition?
• If I am immunosuppressed, should my medications be reviewed to lower my risk?