The Role of PET Scans in Melanoma

Article:

Papai E, Ntoh K, Zhang L, Yu JQ, Olszanski AJ, Villano AM, Porpiglia AS, Reddy SS, Farma JM, Greco SH. The Utility of Preoperative PET/CT in Patients with Clinically High-Risk Melanoma. Ann Surg Oncol. 2025 Dec;32(13):9668-9675.

Understanding PET/CT Scans for Melanoma

What is a PET/CT scan? 

A PET/CT combines two imaging techniques: PET (positron emission tomography) shows cancer activity by detecting areas using high amounts of sugar, and CT (computed tomography) provides detailed anatomical pictures. Together, they can find melanoma that has spread to lymph nodes or distant organs.

When is PET/CT recommended? 

Current guidelines do not recommend routine PET/CT for early or intermediate melanomas (less than 4 mm deep) because these rarely have spread that imaging can detect. For thicker melanomas (over 4 mm deep, called T4), the role of PET/CT is debated.

What this study found 

Researchers looked at 94 patients with thick melanomas (over 4 mm) who had no obvious signs of spread on physical exam. Only 8.5% had unexpected findings on PET/CT, and these changed the treatment plan in 7 of those 8 patients (7.4% of all patients).

The good news: PET/CT rarely showed hidden spread when doctors couldn't feel enlarged lymph nodes.

The concerning news: PET/CT missed cancer in lymph nodes 84.6% of the time—when sentinel lymph node biopsy (removing and examining the first draining node) found cancer, PET/CT had been negative in most cases. This is because PET/CT can only detect tumors about 4–7 mm in size; microscopic cancer deposits are invisible on the scan.

Why this matters

1. Limited sensitivity: PET/CT had only 15.4% sensitivity for detecting lymph node involvement. That means it misses most cases where cancer has spread to nodes microscopically. The negative predictive value was 74%—if your scan is negative, there's still a 26% chance cancer is in your nodes.

2. Good specificity: When PET/CT showed something suspicious, it was correct about half the time (50% positive predictive value). False positives can lead to unnecessary biopsies or surgeries.

3. Clinical exam is key: A thorough physical examination by an experienced doctor remains the most important evaluation tool. PET/CT didn't add much beyond what doctors could detect by examination.

When PET/CT might be useful 

PET/CT may have a role in specific situations:

- When you have clinically enlarged or suspicious lymph nodes (not included in this study but known to benefit from imaging)

- If you're considering neoadjuvant immunotherapy (treatment before surgery)—PET/CT can show extent of disease and help guide this decision

- For surveillance after treatment in higher-stage disease

- If physical exam is difficult (for example, deep lymph node basins)

What changed with PET/CT findings? 

In the 7 patients whose treatment changed: some had additional biopsies before surgery, others went straight to lymph node dissection instead of sentinel node biopsy, and one discovered a separate lung cancer requiring treatment first.

Take Home Message:

For thick melanoma without clinically obvious spread, routine PET/CT before surgery doesn't find hidden disease often enough to justify its routine use. Physical examination and sentinel lymph node biopsy remain the standards. However, PET/CT may be considered on a case-by-case basis—especially if you have concerning symptoms, ambiguous physical findings, or are being evaluated for immunotherapy before surgery