Melanoma Diagnosis: Tests, Biopsy, and What to Expect

Key Takeaways

• The only way to definitively diagnose melanoma is through a biopsy: removing tissue for microscopic examination by a pathologist.

• Dermoscopy significantly improves the accuracy of clinical diagnosis and helps your dermatologist decide which lesions need biopsy.

• Your pathology report provides critical information including Breslow thickness, Clark level, ulceration, and mitotic rate: these numbers directly determine your stage and treatment plan.

• Sentinel lymph node biopsy is a staging procedure, not a treatment, recommended for most melanomas thicker than 0.8 mm to determine whether cancer has reached regional lymph nodes.

• Molecular testing, including BRAF mutation status, is standard for all patients with advanced melanoma and directly shapes treatment decisions.

• A melanoma diagnosis can feel overwhelming, but the diagnostic process gives you and your care team the precise information needed to build the best treatment plan.

How Is Melanoma Diagnosed?

Melanoma diagnosis follows a clear sequence: a visual skin exam, enhanced with dermoscopy, identifies suspicious lesions. A biopsy: the only way to confirm or rule out melanoma, removes tissue for pathologic analysis. The resulting pathology report determines Breslow depth and other features that guide staging. For invasive melanomas, staging tests, including sentinel lymph node biopsy and imaging, assess whether the cancer has spread.

The Skin Exam and Dermoscopy

The diagnostic process typically begins with a visual examination of the skin. During a full-body skin exam, your dermatologist examines the entire skin surface, including the scalp, between the toes, the soles, under the nails, and the genitals, not just sun-exposed areas.

Dermoscopy is a technique in which a handheld device called a dermoscope (or dermatoscope) is used to examine skin lesions under magnification with polarized or immersion lighting. Dermoscopy allows the examiner to visualize pigment patterns, vascular structures, and architectural features in the epidermis and superficial dermis that are invisible to the naked eye. These structures, patterns of pigmented networks, streaks, dots, regression structures, and vessels, follow recognized criteria that correlate with benign versus malignant diagnoses.

Studies consistently show that dermoscopy significantly improves diagnostic accuracy for melanoma compared to naked-eye examination alone. A meta-analysis published in the British Journal of Dermatology found that dermoscopy performed by trained clinicians improved melanoma sensitivity by approximately 27% compared to the naked eye. It also reduces unnecessary biopsies of benign lesions, sparing patients from procedures they don’t need.

Dermoscopy is not a replacement for biopsy, it informs the decision about whether to biopsy, but only pathologic examination of tissue can confirm a diagnosis.

Skin Biopsy: What It Is and What to Expect

A biopsy is the definitive test for melanoma. During a biopsy, the suspicious lesion (or a portion of it) is removed and sent to a pathology laboratory, where a pathologist examines the tissue under a microscope.

Types of biopsy:

Excisional biopsy is the preferred technique for most melanoma-suspicious lesions. The surgeon or dermatologist removes the entire lesion with a narrow margin of surrounding normal tissue. This provides the pathologist with the complete specimen, including the deepest part of the lesion, which is essential for accurate Breslow measurement and staging. Excisional biopsy is typically performed in an office or outpatient surgical setting under local anesthesia.

Punch biopsy uses a circular cutting tool to remove a cylindrical core of tissue. It is appropriate for smaller lesions, flat lesions on difficult anatomical areas, or lesions where excisional biopsy is not immediately feasible. It can adequately sample most lesions when performed through the thickest part of the suspected melanoma.

Shave biopsy involves slicing across the skin to remove a superficial layer of tissue. It is widely used for raised, benign-appearing lesions, but is generally discouraged for melanoma-suspicious lesions because a shallow shave may not capture the base of the lesion, making it impossible to accurately measure Breslow thickness. If a shave biopsy inadvertently reveals melanoma, repeat excision is typically required to obtain adequate margins and complete staging information.

What the procedure feels like. Local anesthetic is injected to numb the area before any biopsy. Most patients feel pressure during the procedure rather than pain. The biopsy site typically heals within 1–2 weeks. Stitch-based closures are common for excisional biopsies; punch biopsies may be closed with a single stitch or left to heal on their own. Discomfort is generally mild and manageable with over-the-counter pain relievers.

Results timing. Most biopsy results return within 5–10 business days, though more complex cases may take longer if special stains or second opinions are sought. Your provider should contact you when results are available regardless of outcome.

Reading Your Pathology Report

If your biopsy is positive for melanoma, the pathology report will contain several key pieces of information. Understanding these terms helps you participate fully in your care:

Breslow thickness. Measured in millimeters from the top of the epidermis to the deepest point of tumor invasion. This is the most important single number in your pathology report and directly determines T-stage. Lower is better.

Clark level. An older anatomical staging system describing how deeply the melanoma has penetrated the layers of the skin (I through V). While largely supplanted by Breslow thickness in current staging, it may appear on your report. Level I = confined to epidermis; Level V = invasion into subcutaneous fat.

Ulceration. Whether the skin surface over the tumor is intact or broken down. Ulceration is a sign of biological aggressiveness and elevates your stage, for example, a 1–2 mm tumor is Stage IIA without ulceration but Stage IIB with ulceration.

Mitotic rate. The number of actively dividing cells per square millimeter of tumor tissue. Higher mitotic rates indicate more rapidly proliferating tumors and are associated with worse outcomes. Reported as per mm².

Surgical margins. Whether any melanoma cells are present at the edge of the excised tissue. Positive margins mean cancer cells extend to the edge of the removed specimen and that re-excision is needed to achieve clear margins. Negative margins mean a rim of normal tissue surrounds the tumor.

Histologic subtype. Which growth pattern the melanoma displays, superficial spreading, nodular, lentigo maligna, acral lentiginous, etc.

Lymphovascular invasion. Whether cancer cells are present within blood vessels or lymphatic channels in the specimen, a feature associated with higher risk of spread.

Do not hesitate to ask your dermatologist or oncologist to walk through your pathology report with you. These numbers are your numbers, and understanding them helps you ask better questions and make more informed decisions.

Staging Tests: Is the Melanoma Still Localized?

Once melanoma is confirmed, the next question is whether it has spread beyond the primary skin site. The extent of staging workup depends on the thickness and features of the primary tumor.

Physical examination. Your doctor will carefully examine the regional lymph node basins draining the area of the primary melanoma, feeling for enlarged, firm, or tender nodes. Nearby skin will also be inspected for satellite lesions (small tumor deposits near the primary site) or in-transit metastases (tumor deposits in the lymphatic channels between the primary site and lymph nodes).

Lymph node ultrasound. High-resolution ultrasound of the regional lymph node basin is sometimes used when nodes feel enlarged or when clinical assessment is uncertain.

CT scan (computed tomography). CT of the chest, abdomen, and pelvis is typically ordered when there is concern about regional or distant spread, for Stage IIB or higher, or when sentinel node biopsy is positive. CT detects nodal involvement and visceral metastases in the lungs, liver, and other organs.

PET/CT scan. A PET scan combines metabolic imaging (using a radioactive glucose tracer taken up by rapidly dividing cells) with CT anatomical imaging. PET/CT is more sensitive than CT alone for detecting distant metastases and is commonly used for staging Stage III and IV melanoma. It can identify sites of metastasis in lymph nodes, bones, and soft tissue that CT may miss.

MRI (magnetic resonance imaging). MRI of the brain is typically ordered when there is concern about brain metastases, especially in Stage IV disease. Brain MRI may be performed as part of initial staging in Stage III or higher, and periodically during treatment for patients with Stage IV disease.

For Stage I melanoma without high-risk features, a sentinel lymph node biopsy may be the only staging procedure needed beyond the primary excision. Routine imaging is generally not recommended for Stage IA or IB without additional risk factors, as the yield is low and false positives cause unnecessary anxiety and follow-up procedures.

Sentinel Lymph Node Biopsy

Sentinel lymph node biopsy is a surgical procedure used to assess whether melanoma has spread to the regional lymph nodes, the first lymph nodes that drain the area of the primary tumor. It is a staging procedure, not a therapeutic one, and it provides critical information that changes staging and guides treatment decisions.

Who should have it? Current guidelines generally recommend sentinel node biopsy for melanomas with a Breslow thickness greater than 0.8 mm. For melanomas between 0.6 and 0.8 mm with additional high-risk features (such as ulceration or high mitotic rate), it may also be recommended. For melanomas 0.8 mm or thinner without other risk factors, the yield is low and the procedure is typically not recommended.

How it works. On the day of the procedure, a small amount of radioactive tracer and/or blue dye is injected near the primary biopsy site. The substance travels through the lymphatic system to the first-draining lymph node (or nodes), the sentinel node. A nuclear medicine gamma camera identifies which node has taken up the tracer, guiding the surgeon to the correct node(s) for removal. The procedure is performed in an operating room under local or general anesthesia.

What the result means. If the sentinel node is negative (no melanoma cells detected), the cancer is very likely still localized, and no further lymph node surgery is needed. If the sentinel node is positive (melanoma cells found), the staging changes from Stage II to Stage III, triggering discussion of adjuvant systemic therapy to reduce the risk of recurrence.

A positive sentinel node does not necessarily mean that all regional lymph nodes are involved. Completion lymph node dissection, removing all nodes in the basin, is no longer routinely performed for microscopic sentinel node positivity, as trials showed it did not improve survival while adding significant morbidity (lymphedema).

Molecular and Genetic Testing

Molecular testing of the melanoma tumor is now a standard part of the diagnostic workup for patients with Stage III or IV disease, and increasingly for Stage IIB/IIC.

BRAF V600E/V600K mutation testing. Approximately 40–50% of cutaneous melanomas carry a BRAF mutation, most commonly BRAF V600E. This result is essential before starting systemic treatment because BRAF-mutated tumors are eligible for targeted therapy with BRAF and MEK inhibitor combinations, a highly active and rapidly effective treatment class. BRAF testing is performed on tumor tissue (biopsy or surgical specimen) and is a standard-of-care step before initiating treatment for advanced melanoma.

NRAS mutation. NRAS is mutated in approximately 15–20% of melanomas. While there are no NRAS-specific targeted therapies currently approved for melanoma, NRAS status is relevant for understanding tumor biology and may affect clinical trial eligibility.

C-KIT mutations. C-KIT mutations are more common in acral lentiginous and mucosal melanoma subtypes. In patients whose tumors are C-KIT mutated, C-KIT inhibitors (such as imatinib) may have activity and are sometimes used off-label or in clinical trials.

Tumor mutational burden (TMB). Tumor mutational burden is a measure of how many mutations are present in the tumor genome. Higher TMB has been associated with greater likelihood of response to immunotherapy across multiple cancer types. TMB testing is available as part of comprehensive molecular profiling panels.

PD-L1 expression. PD-L1 expression on tumor cells has been studied as a potential predictor of response to PD-1 checkpoint inhibitor immunotherapy, though its predictive value in melanoma is less clear-cut than in some other cancer types. It may be reported as part of comprehensive profiling.

Comprehensive molecular profiling, testing for multiple relevant mutations simultaneously, is available at most cancer centers and can be performed on tissue from your original biopsy or surgical specimen. Discuss with your oncologist whether full molecular profiling is appropriate for your situation.

For information on what happens after diagnosis and how your stage is determined, see melanoma stages. For information on treatment based on your diagnosis, see melanoma treatment. For information about what to look for before a diagnosis, see melanoma symptoms and types of melanoma.

A melanoma diagnosis is the beginning of a path, not the end of one. If you want to explore your full range of options, including clinical trials, North’s trial finder can help.

Frequently Asked Questions

How is melanoma diagnosed?

Melanoma is diagnosed through a combination of clinical examination, dermoscopy, and, definitively, biopsy. A dermatologist examines suspicious lesions visually and with dermoscopy to assess features associated with melanoma. If a lesion is concerning, a biopsy removes tissue for examination under a microscope by a pathologist. The pathology report confirms whether melanoma is present and provides key staging information including Breslow thickness, ulceration, and mitotic rate. No blood test, imaging study, or dermoscopy result alone can confirm melanoma, only tissue pathology can.

What happens during a skin biopsy for melanoma?

The area around the suspicious lesion is numbed with local anesthetic, most patients feel only mild pressure during the procedure itself. The dermatologist or surgeon removes the lesion (excisional biopsy) or a portion of it (punch biopsy) and closes the wound with sutures if needed. The tissue sample is sent to a pathology laboratory. Results typically return within 5–10 business days. The procedure is routine, outpatient, and most patients return to normal activity the same day.

What does a melanoma pathology report include?

A melanoma pathology report will include: confirmation of the diagnosis, Breslow thickness (depth in millimeters, the most important prognostic measurement), Clark level, presence or absence of ulceration, mitotic rate, surgical margin status (clear or positive), histologic subtype, and whether lymphovascular invasion is present. Together, these features determine T-stage and guide decisions about sentinel lymph node biopsy, re-excision margins, and adjuvant treatment discussions.

What is a sentinel lymph node biopsy?

Sentinel lymph node biopsy is a surgical procedure in which the first lymph node(s) draining the area of a primary melanoma are identified using a radioactive tracer and/or blue dye, removed, and examined for the presence of melanoma cells. It is a staging procedure, the results change the stage from II to III if positive, triggering discussion of adjuvant therapy. It is generally recommended for melanomas thicker than 0.8 mm. The procedure is performed under anesthesia and is typically a same-day surgery.

Do I need a PET scan for melanoma?

Not for early-stage melanoma. For Stage IA and IB melanoma without additional risk factors, routine imaging is generally not recommended because the probability of distant spread is very low and false-positive scans can lead to unnecessary anxiety and procedures. A PET scan is typically ordered for Stage IIB or higher, when sentinel node biopsy is positive (Stage III), or when there are clinical findings suggesting possible spread. For Stage IV disease, PET/CT is a standard part of staging and response assessment.

References

1. National Cancer Institute. Melanoma Treatment (PDQ), Patient Version. https://cancer.gov/types/skin/patient/melanoma-treatment-pdq

2. American Academy of Dermatology Association. Melanoma: Diagnosis and Treatment. https://www.aad.org/public/diseases/skin-cancer/types/common/melanoma/diagnose-treat

3. National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Melanoma, Cutaneous. https://www.nccn.org/patientresources/patient-resources/guidelines-for-patients/guidelines-for-patients-details?patientGuidelineId=21

4. Vestergaard ME, Macaskill P, Holt PE, Menzies SW. Dermoscopy compared with naked eye examination for the diagnosis of primary melanoma: a meta-analysis of studies performed in a clinical setting. Br J Dermatol. 2008;159(3):669-676. https://pubmed.ncbi.nlm.nih.gov/18616769.

5. Morton DL, Thompson JF, Cochran AJ, et al. Final trial report of sentinel-node biopsy versus nodal observation in melanoma (MSLT-I). N Engl J Med. 2014;370(7):599-609. https://pubmed.ncbi.nlm.nih.gov/24521106.

6. Faries MB, Thompson JF, Cochran AJ, et al. Completion dissection or observation for sentinel-node metastasis in melanoma (MSLT-II). N Engl J Med. 2017;376(23):2211-2222. https://pubmed.ncbi.nlm.nih.gov/28591523.