PET Scans Clear Hurdle for Merkel Cell Dx
By Ed Susman, Contributing Writer, MedPage Today
Published: November 01, 2012
Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner
BOSTON – Use of fluorodeoxyglucose positron emission tomography (FDG-PET) imaging has an impact on how Merkel cell carcinoma patients are diagnosed or treated in about a third of cases, researchers said here.
In fact, 64 of 194 scans (33%) performed on 123 consecutive patients with Merkel cell carcinoma had a 'high' impact -- defined as a change in treatment or treatment plans -- on care, Michael MacManus, MD, of the Peter MacCallum Cancer Centre in Melbourne, Australia, reported at the American Society of Radiation Oncology meeting.
That result broke down as follows, according to McManus:
- In 102 scans performed for staging, 23 (23%) had 'high' impact and 15 (15%) had 'medium' impact
- In 39 scans performed to assess response to disease, 17 (44%) had high impact and none had 'medium' impact
- In 53 scans performed for re-staging at the time of suspected relapse, 24 (45%) had 'high' impact and 6 (11%) had medium impact
"Merkel cell carcinoma is a rare cutaneous neuroendocrine carcinoma," MacManus said. The disease arises in hair follicles and appears to be related to ultraviolet light and Merkel cell polyoma virus. The disease is easily pinpointed with PET imaging, and yet the largest study to date included a mere 12 patients, he said.
The primary endpoint of the study was to show that PET would have at least a 10% high impact or a 25% high or medium impact. MacManus said his finding met those criteria (P<0 .001=".001" b="b">
Among the other findings in the study, the researchers found that of the 23 staging PET scans with 'high impact,' 14 resulted in a change in treatment, 5 caused a change in treatment intent, and 4 resulted in changes in both treatment modality and radiotherapy techniques.
MacManus also noted that 22% of patients had incongruent staging between conventional and PET staging. The use of PET scans upstaged 17 patients -- four because of occult distant disease and 13 because of occult nodal disease.
On the other hand, PET imaging downstaged five patients – two of whom were suspected of having Stage 4 disease and 3 who were thought to have had Stage 3 disease, MacManus said.
