How is Skin Cancer Diagnosed?

This is the sixth page in the Understanding Skin Cancer Guide. This guide was developed by the HealthTree Education Team and was last updated and reviewed on May 14, 2026.

If your doctor thinks you may have skin cancer, there are several tests and procedures that can confirm a diagnosis. Diagnosis relies on a combination of your symptoms, a physical skin examination, and test results.

This page lists all of the different tests that may be needed. Some are used to confirm a skin cancer diagnosis. Others are used to learn more about the cancer, such as whether it has spread, and can help guide treatment. Some of these tests may also be used to monitor how well treatment is working. You may not have all of the tests on this list.

Talk to your care team if you have questions about which tests you received and what the results mean for your diagnosis.

Biopsy

A biopsy is the only way to confirm a diagnosis of skin cancer. During a biopsy, a sample of tissue is removed from the suspicious area of skin and examined under a microscope. There are several types of skin biopsies:

• Shave biopsy. A small blade is used to shave off the top layers of skin. This technique is commonly used for raised or superficial lesions.
• Punch biopsy. A circular tool is used to remove a small, deep core of skin tissue. This is used to examine deeper skin layers.
• Excisional biopsy. The entire suspicious lesion is surgically removed, along with a small margin of surrounding normal skin. This is often done when melanoma is suspected.
• Incisional biopsy. Only part of a large lesion is removed for examination.

A pathologist then analyzes the sample to determine if cancer cells are present, and if so, what type of skin cancer it is. A pathologist is a doctor who specializes in examining tissue samples.

Imaging tests to diagnose skin cancer

Imaging tests create pictures of the inside of the body and are used to check whether skin cancer, particularly melanoma, has spread beyond the skin:

• Computed tomography (CT). A CT scan may be used to check whether melanoma has spread to the lymph nodes, lungs, liver, or other organs.
• Positron emission tomography (PET). A PET scan can be used to look for cancer spread throughout the body.
• Magnetic resonance imaging (MRI). An MRI may be used to evaluate whether melanoma has spread to the brain or spinal cord.
• Ultrasound. An ultrasound may be used to evaluate lymph nodes near the site of the primary tumor.
• Chest X-ray. May be used to check whether cancer has spread to the lungs.

Lymph node evaluation

For melanoma and some high-risk squamous cell carcinomas, evaluating the lymph nodes is an important part of staging:

• Sentinel lymph node biopsy (SLNB). A procedure used to determine whether cancer has spread to the nearest lymph node(s). A radioactive substance and/or dye is injected near the tumor to identify the sentinel node(s), which are then removed and examined. If the sentinel node is negative for cancer, the remaining lymph nodes are likely cancer-free and do not need to be removed.

Blood tests to diagnose skin cancer

Blood tests are not routinely used to diagnose skin cancer, but may be used in monitoring or staging:

• Lactate dehydrogenase (LDH). An elevated LDH level in the blood can be a sign of advanced melanoma and may affect staging.
• Complete blood count (CBC) and comprehensive metabolic panel (CMP). These tests check overall health and organ function, which can be affected by cancer or its treatment.

Biomarker and genetic tests to diagnose skin cancer

Biomarker testing looks for specific changes in the cancer cells that can help guide treatment decisions. For skin cancer, important tests include:

• BRAF mutation testing. About 50% of melanomas have a mutation in the BRAF gene (most commonly BRAF V600E). This test is important because BRAF-mutated melanomas can be treated with BRAF inhibitor drugs.
• PD-L1 testing. Checks for expression of the PD-L1 protein, which may predict response to immunotherapy (checkpoint inhibitors).
• Tumor mutational burden (TMB). A measure of the number of mutations in the cancer's DNA. High TMB may predict a better response to immunotherapy.
• NRAS and other mutation testing. Other mutations such as NRAS, KIT, and NTRK may affect treatment eligibility for certain targeted therapies.
• BRCA and other hereditary gene testing. May be recommended for patients with a strong family history of melanoma or associated cancers.