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Can PET Scan Tell Type of Tumor?

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Last Modified: October 1, 2006

Dear OncoLink "Ask The Experts,"

My father had a surgery for stomach cancer three years ago. Recently, he was found to have some tumor around his neck. His PET scan result shows that he has tumor. Can the PET test check out whether the tumor is malignant or not? Can it also tell whether the tumor around the neck indicates the same stomach cancer again, or if it is a lymph node tumor that has nothing to do with the old stomach cancer?

Carolyn Vachani RN, MSN, AOCN, OncoLink's Nurse Educator, responds:

A PET scan can help determine if a lesion is "suspicious" for cancer (malignancy), as opposed to something benign. However, it cannot tell you with 100% certainty that it is indeed cancer, nor can it tell you what type of cancer that lesion represents. Your father will need a biopsy to determine if the tumor around his neck is in fact cancer, and if so, to determine what type of cells the neck mass is made up of -- either the stomach cancer, or something different.

In general, when a patient with a history of some type of cancer later develops a cancerous lymph node, the cancer cells in that lymph node typically (though not always) do not represent a "lymph node tumor", but rather are more likely to represent the original primary tumor, which then metastasized (spread) secondarily to the lymph node(s).