By Sandra Gordon

At his three-month follow up computerized tomography (CT) scan last year‚ Vince Gordon (no relation)‚ a sales vice president in Greenwood Village‚ Colorado‚ received bad news.

“The CT scan indicated that my melanoma had progressed from stage three to stage four‚ which was obviously frightening‚” says Gordon‚ 51‚ who was initially diagnosed in 1998. To confirm the findings‚ Gordon underwent a positron emission tomography (PET) scan‚ the latest technology now used in cancer staging‚ restaging‚ and follow up. Fortunately‚ the PET scan proved the CT scan wrong. His cancer hadn’t spread‚ saving him from undergoing unnecessary treatment. “What a relief‚” Gordon says.

First used in brain imaging in the 1960s‚ PET is revolutionizing the way cancer is diagnosed and staged. “With PET‚ you have the potential to detect cancer at a very early stage‚” says Lee P. Adler‚ MD‚ chief of molecular imaging at the Fox Chase Cancer Center in Philadelphia‚ Pennsylvania. That’s because CT‚ magnetic resonance imaging (MRI)‚ and ultrasound take images of anatomy‚ changes at the tissue level that are determined to be abnormal based on size. PET captures physiology at the molecular level.

After some therapies‚ a cancerous tumor may first change metabolically by using more glucose‚ the sugar that all cells require to thrive and survive‚ before it changes in size‚ explains Barbara Galen‚ MSN‚ program director with the Biomedical Imaging Program at the National Cancer Institute in Bethesda‚ Maryland‚ adding that that is what makes PET such a cutting–edge tool in cancer diagnosis and management. PET can detect early metabolic (glucose) changes before a tumor has grown to the point at which it shows up on conventional tests‚ perhaps eliminating the need for a biopsy‚ additional CT scans or MRIs‚ and surgery.

For example‚ a lymph node in most areas of the body greater than or equal to 1 to 1.4 centimeter is considered abnormal‚ says Dr. Adler. “With CT‚ you could have a nine–millimeter lymph node that would be read as normal by conventional criteria. But the PET scan could indicate cancer if there were changes on the molecular level.”

How PET Works
A PET scan begins with an injection of a trace amount of the Food and Drug Administration–approved pharmaceutical [18F] fluoro–2–deoxyglucose (FDG)‚ a radioactive glucose molecule that travels to every cell in the body. After the 18F–FDG is administered‚ the patient is asked to lie still for about an hour in a dark‚ quiet room and avoid talking to prevent the compound from concentrating in the tongue and vocal cords.

The hour waiting time allows the 18F–FDG to be absorbed and released from normal tissue. After emptying the bladder‚ the patient lies on a bed that moves slowly and quietly through a tube that is similar to a CT scan. A whole–body scan‚ from the base of the skull to the pelvis‚ typically takes 30–90 minutes.
Because cancer cells rapidly divide‚ and hence absorb more 18F–FDG than noncancerous cells‚ they show up brighter on the PET scan‚ says Elissa L. Kramer‚ MD‚ director of nuclear medicine at Tisch Hospital in New York City. After a PET scan‚ the patient can return to home or work and continue with the remainder of the day.

PET Isn't Perfect
The PET scan isn’t appropriate for every type of cancer. In fact‚ the Centers for Medicare & Medicaid Services (CMS)‚ the government agency that provides health insurance for more than 74 million Americans through Medicare‚ Medicaid‚ and State Children’s Health Insurance Program‚ only covers PET for diagnosing‚ staging‚ and restaging a select group of cancers: non—small–cell lung‚ esophageal‚ colorectal‚ lymphoma‚ melanoma‚ and head and neck. CMS‚ which sets the tone for third–party insurance carriers‚ recently added breast cancer (staging and restaging only) to the list. A physician‚ however‚ may suggest PET under other circumstances‚ in which case‚ getting insurance pre–approval is often necessary.

Shelley Bayewitch‚ 48‚ of Bellmore‚ New York‚ underwent a PET scan to follow the metastases of her breast cancer to her bone marrow‚ which recently recurred after a 10–year remission. “PET isn’t normally done in this situation‚ but they’re trying to use my PET scan as a baseline to see if in six months my cancer is getting better or worse‚”says Bayewitch‚ who had no trouble getting PET approved by her insurance carrier.

If insurance rejects PET‚ it will cost the patient in the range of $2‚500-$5‚000.
“PET is most useful if you’re trying to make a decision about whether a patient is a candidate for surgery‚” says Dr. Adler. But it isn’t always appropriate or necessary. “Suppose a patient has been newly diagnosed with lung cancer and it?s obvious from the CT scan that the patient isn’t a candidate for surgery. Why would you do the PET if you’re going to give the patient systemic therapy anyway?” says Dr. Adler.

Moreover‚ PET isn’t perfect. It can register false positives in a variety of situations. Scar tissue from lung infections such as tuberculosis‚ histoplasmosis‚ spinal degenerative or joint disease‚ a broken bone that’s healing‚ and sites of inflammation can show up as falsely “hot” on a PET scan‚ which can confuse radiologists. To reduce the likelihood of false positives‚ a complete medical history is taken before the scan‚ says Galen.

When used correctly‚ PET can be very useful because it’s able to detect earlier the extent of disease for the initial staging and determine if there has been recurrence in other parts of the body‚ says Elizabeth Yung‚ MD‚ director of Winthrop University’s PET Imaging Center and Nuclear Medicine in Mineola‚ New York. And with reimbursement programs now in place‚ PET is gaining ground in medical facilities across the country. It’s estimated that more than 500 medical facilities in the United States are now equipped to provide PET scanning services. On the horizon are combination PET/CT scans that have the potential to further clarify the window to the body’s molecular activity.

“With PET/CT‚ you can improve PET’s sensitivity by 5–10%. That doesn’t sound like much‚ but it’s actually a fantastic improvement for an already good test‚” says Dr. Adler.