University of Iowa researchers developed a new imaging approach for identifying a rare form of thyroid cancer typically hard to diagnose. Malik Juweid, MD, radiology nuclear medicine specialist at University of Iowa Hospitals and Clinics, talk about this new approach:

What are the symptoms or signs of thyroid cancer?

The typical symptoms of thyroid cancer are usually a lump on the tyroid—that’s in the region of the Adam’s apple of the neck—or in the neck nodes. These lumps are usually painless but sometimes can cause pain or at least discomfort, especially when they are large. With further tumor growth, however, symptoms like hoarseness, difficulty swallowing or breathing may develop.

How is thyroid cancer typically detected or diagnosed?

The patients with the typical symptoms I just mentioned usually seek the doctor, and if they don’t, they should. It would be best to see an endocrinologist, but an internist or general practitioner can refer them to the needed specialist.

The doctor then performs a physical exam and typically orders and ultrasound of the thyroid. The ultrasound helps reveal the nature of the nodule—for example, whether it is cystic or solid—and provides a preliminary assessment whether the nodule represents a benign condition—such as inflammation or possibly cancer.

However, the final diagnosis is only made after a biopsy of that nodule has been done with histopathologic examination. Sometimes even surgical removal of the nodule will become necessary for a more comprehensive histopathology examination and more a more reliable diagnosis.

Why is poorly differentiated thyroid cancer or PDTC hard to diagnose?

It’s because of the lack of consistent expression of we call immunohistochemical markers on the tissue that is taken out to examine this cancer. These markers are, for example, thyroglobulin, and they would point to some degree of thyroid tissue differentiation. If this marker is not there, it will become very, very hard. Also there is a lack of consensus on histopathologic definition among the various pathologists.

What imaging technique did you and other colleagues use to help detect PDTC in the recent study?

In our study, we dealt with a tumor in the thyroid and neck lymph nodes that cannot be removed surgically, it’s called unresectable, where the origin of that cancer was unknown. All we knew was that the tumor was a fully differentiated adenyl carcinoma, but that it could be a primary thyroid cancer or just metastases or secondary cancer coming from cancer in other organs, such a the pancreas, lungs, or colon. We knew that only thyroid cancer cells could concentrate radioiodine to some degree, depending on their differentiation. Since the patient still had some thyroid tissue not invaded by the tumor, the internal stimulus for the thyroid cancer cells to take up radioiodine, which is known as thyroid stimulating hormone, or TSH, was minimal. Therefore we gave the patient a genetically engineered or external TSH by intramuscular injections, and then managed to stimulate the poorly differentiated cancer to take up radioiodine. In this way we’ve proven that the cancer was indeed of thyroid origin, mainly poorly differentiated thyroid cancer.

So is radioiodine currently used in treating cancer?

Yes. Currently almost always the thyroid is taken out by the surgeon, but there is also nearly always a small residual amount of thyroid tissue left, which could harbor some cancer cells. Here we use radioiodine to kill these remaining cancer cells and thus minimize the chance of the tumor coming back.

Sometimes the tumor has also spread beyond the thyroid, usually to neck lymph nodes, but also occasionally to the lungs or bones. In this case, radioiodine represents a very effective treatment which often can completely eliminate and cure the cancer or, at least, delay its growth for years. When we use radioiodine in patients with the thyroid removed—again, these are the vast majority of patients—we do not need to give extra TSH, because there is already stimulation of the internal TSH. In those cases where the thyroid cannot be removed, one might need to use extra TSH for treatment, but this needs to be done with extreme caution in a hospital setting and with very close monitoring of the patient, both clinically and by using the biochemistry lab.

What does the recent study suggest with regard to diagnosing and treating poorly differentiated thyroid cancer?

Again, the use of this scan is reserved for those cases where the thyroid cannot be surgically removed, and where histopathology cannot clearly determine whether the tumor is of thyroid origin or if it’s poorly differentiated, undifferentiated, or so called anaplastic. Here the use of stimulated scans will be helpful to clarify the diagnosis by showing radioiodine uptake in the tumor if it’s truly a poorly differentiated thyroid cancer.

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Malik Juweid, MD