In an era of increased treatment options for high-grade tumors, failure to accurately identify tumor types exposes patients to avoidable risk. Patients with tumors classified as occult, or cancer of unknown primary, might receive inappropriate therapy or miss out on potentially beneficial treatment.
Rondell Graham, M.B.B.S., an anatomic and molecular pathologist at Mayo Clinic, co-led a molecular oncology tumor board session at CAP19, and subsequently spoke with CAP Today. Focusing on immunohistochemistry, Dr. Graham outlined a "safe, stepwise approach" to the workup of occult cancer:
- Determine the lineage. Dr. Graham listed several tests he uses to place an occult tumor in one of two broad categories: a common carcinoma type that pathologists can recognize (for example, adenocarcinoma), or a high-grade or poorly differentiated carcinoma type that pathologists can't specifically identify.
- Narrow the differential. Once a cancer type is identified, additional tests can further define the diagnosis. For example, keratin 7 and keratin 20 testing can narrow the differential diagnosis for carcinomas.
- Refine the search for a carcinoma subtype by testing for various markers, such as GATA3. However, Dr. Graham cautioned that many different tumor types can be positive for GATA3 and other markers.
The five most common occult primaries identified at autopsy are lung cancer, pancreatobiliary malignancy, other gastrointestinal tumors, breast cancer, and ovarian carcinoma, Dr. Graham reported. “You want to make sure that when you finish your workup and you are ready to sign it out as a cancer of unknown primary, that you considered or excluded these possibilities as much as possible,” he said.