Source: Elsevier Global Medical News

Routine use of positron emission tomography/computed tomography scans can detect locoregional recurrences of squamous cell carcinoma of the head and neck before they became clinically apparent, according to a retrospective chart review of 234 patients who had been treated with chemoradiation between 2006 and 2010.

The finding suggests that routine use of positron emission tomography/computed tomography (PET/CT) may improve the outcome of salvage therapy, said Dr. Yasir Rudha, who reported the study at the Multidisciplinary Head and Neck Symposium sponsored by the American Society for Radiation Oncology.

PET/CT was associated with a high false positive rate, which should be considered when ordering radiological exams and biopsies, but a negative post therapy PET scan appears to be an excellent predictor of freedom from future locoregional recurrence, said Dr. Rudha of St. John Hospital/Van Elslander Cancer Center, Grosse Pointe Woods, Mich.

The technology is relatively new, and its use for routine follow-up in patients with head and neck cancer is still controversial, he acknowledged. “Only a few publications have reported the value of PET examination at a fixed time interval after the end of treatment,” he said. “PET scan is often ordered in our hospital as a routine surveillance tool following successful completion of treatment.”

The review of charts for all 234 patients identified 45 who had achieved clinical no-evidence-of-disease status at the time of post treatment imaging. In this group, PET/CT scanning at 6-9 weeks identified 15 patients with abnormalities that required further evaluation. Of those, eight patients (53%) were proven to have malignancies based on biopsy findings: six showed occult persistent disease at the primary site, and two were diagnosed with regional lymph node recurrence and colon cancer, respectively.

In the remaining seven cases, imaging findings were shown to represent false positive results with unnecessary work-up and/or biopsy evaluation. All patients who had negative PET/CT scans remained free from locoregional relapse at the time of last follow-up.

Thus, Dr. Rudha said the true positive rate for routine PET/CT surveillance in head and neck cancer patients was estimated as 8/15, or 53%, and the false positive rate as 7/15, or 46%.

”With malignancies found in 53% of abnormal scans in this study, our research proves that PET/CT scans are valuable as routine follow-up and as a surveillance method for head and neck cancer patients … However, since the rate of false positives was 46%, caution should be shown when ordering biopsies after abnormal scans to prevent excessive unnecessary biopsies,” he said.

During a press briefing, Dr. Rudha said that the 46% false positive rate was lower than what he and his colleagues expected. “Actually we expected the false positive ratio to be about 90%,” he said.

In an interview, he said that at his institution patients with positive PET/CT scans at 6-9 weeks post surgery are followed in a variety of ways, depending primarily on the PET standard uptake volume (SUV). If low, the patient might undergo another PET scan at about 3 months. But if SUV is high, the patient would likely be referred for another test such as magnetic resonance imaging, ultrasound, or biopsy at the site of recurrence.

However, if the post surgery PET/CT scan is negative, “according to this research, it gives a great indication that the patient is free from disease and the treatment is successful.”

PET/CT is being evaluated in a variety of different situations, said Dr. David Raben, professor of radiation oncology at the University of Colorado, Denver. “We’re still looking at programs that are combining PET/CT imaging with functional DCI/MRI imaging in part to help oncologists find the tumor volume and define how to plan our treatments in regard to what the target volumes are both on the ipsilateral and contralateral side of the neck,”

”In the post treatment setting, it’s been absolutely critical for us in terms of determining who should go on to further evaluation or who could be watched carefully. For instance, a University of Maryland group has shown quite nicely that in patients who have a clinical complete response and a complete response by PET imaging, almost all those patients do not need a neck dissection (Head Neck 2010;32:46-52). … That’s a significant savings in health care costs, whereas in the past, almost all of those patients 10-15 years ago would have gone on to a neck dissection,” he said.

The current study also offers important data, Dr. Raben continued. “I believe 6 weeks is too early. We recommend a minimum of 8 weeks, preferably 12 weeks post treatment, to allow inflammation to subside,” he said. “That may help reduce the false positive rate. I think use of PET/CT continues to evolve, and hopefully additional functional imaging studies will help us nail down which patients need to go on to further treatment or biopsy.”

Dr. Rudha and his coauthors and Dr. Raben stated that they had no disclosures.

This news story was resourced by the Oral Cancer Foundation, and vetted for appropriateness and accuracy.