The Role of PET in Melanoma
Dear OncoLink "Ask The Experts,"
My Aunt (age 58) just got diagnosed with Malignant Melanoma on the back of her shoulder. I think it is a good idea for her to get tested to make sure it did not spread to her lymph nodes and lungs. Would a PET scan be the best way to detect the spread of cancer to my Aunts lymph nodes and lungs? Are there any other tests available? Is the University of Penn the only place in the South Jersey/Philadelphia area that performs PET scans? How can my Aunt get an appointment and is the wait long?
Peeyush Bhargava, MD, Chief Fellow in the Department of Nuclear Medicine at the University of Pennsylvania, responds:
Patients with melanoma are classified on the basis of the depth of invasion of the skin by the melanoma (on biopsy). Detection of spread of cancer to the lymph nodes is very important in patients with melanoma.In patients with early stage melanoma, this is determined by lympho-scintigraphy. This procedure identifies the first lymph node, which drains the area of the skin where the melanoma is located. If this lymph node is free of cancer (on biopsy), the other lymph nodes are considered free of disease and the patient is followed up as appropriate. In early stage melanoma, FDG PET has limited role in staging the lymph nodes as it cannot pick up micro-metastasis.
In patients with high-risk melanoma and recurrent melanoma, FDG PET imaging is a useful non-invasive test for detection of sub clinical lymph nodes and metastasis. It is also very useful in evaluating suspicious findings on CT scan or MRI.
Below are the images of a patient with history of melanoma. Patient's melanoma was located on the left upper back. The primary cancer lesion and the draining lymph nodes in the left armpit were removed. On a recent follow up CT scan (images 1 and 2) two lesions are seen in the liver (red arrows). The patient also felt a nodule beneath the skin, in the left forearm. Image 3 is from the MRI, which shows the nodule (red arrow). The lesions in the liver and the nodule are all suspicious for metastasis. Image 4 and Image 5 are images from the whole body PET scan, which show a focus of intense activity located in the left forearm and two foci in the liver (red arrows). These lesions correspond to the lesions described earlier. PET scan confirmed them to be metastatic lesions. This case illustrates the importance of PET scans in evaluating recurrent and suspicious lesions in patients with melanoma. Cancer cells are more active than normal cells and take up more of the radioactive material (FDG) compared to the other tissues.
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