Post-Treatment PET Scan Results Correlate Strongly With Survival in Unresectable Non–Small-Cell Lung Cancer

EAST MELBOURNE, Australia—Positron emission tomography (PET) response to radical chemoradiotherapy or radical radiotherapy can be used to separate non–small-cell lung cancer (NSCLC) patients into groups with widely differing survival probabilities, Michael P. MacManus, MD, reported at the 36th ASCO Annual Meeting.

Although results are preliminary and need to be confirmed at other centers, they indicate that PET may identify patients suitable for salvage therapy, said Dr. MacManus, associate professor of radiation oncology, Peter MacCallum Cancer Institute, East Melbourne, Victoria, Australia.

The study was conducted to investigate the correlation between a post-treatment fluorine-18 fluorodeoxyglucose PET (F-18 FDG PET) scan and survival in NSCLC patients who had been treated with radical radiotherapy alone or chemoradiotherapy.

“The secondary aim was to see if we could delineate a subgroup of patients that could potentially benefit from additional therapy,” Dr. MacManus said.

The 56 NSCLC patients in this study were all part of a prospective lung imaging study. All patients had a pretreatment PET scan, and all patients but two, who received 50 Gy, received 60 Gy of external beam RT and had a follow-up PET scan at a median of 70 days after completion of treatment.

Patients were conventionally staged, then received a PET scan. If extensive disease was indicated by the PET scan, this was verified by biopsies or by further imaging procedures, and if verified, patients received palliative therapy.

Eligible patients had stage IA to IIIB disease. Their tumors were medically or surgically inoperable, ECOG status was generally less than 2, with weight loss generally less than 10%.

Treatment delivered was radical radiotherapy plus chemotherapy in 44 cases, and radical radiotherapy alone in 12 cases.

PET Response

The PET response was evaluated qualitatively. “The pretreatment scan and a post-treatment scan were coregistered on the screen, and the nuclear medicine physician made a qualitative evaluation of the response,” Dr. MacManus said.

PET response categories include complete response, which means no abnormal FDG uptake at any tumor site; partial response, which is reduction of FDG at known tumor sites; no response, which indicates no change; and progressive disease, indicating increased FDG at a known tumor site or the appearance of any new tumor site.

Patients generally had a good performance status, and the major histology was squamous cell carcinoma, with a large component of adenocarcinoma, Dr. MacManus said.

Survival was measured from the date of the PET scan, which was, on average, 4 months after the initiation of therapy, he said. At 12 months, survival was 58%, and at 2 years, 48%.

“We were surprised that such a large percentage of our patients got what appeared to be a complete response on their PET scans, 43%,” Dr. MacManus said. Forty-one percent of the patients appeared to achieve a partial response, 7% of the patients had no response, and 9% had progressive disease.

For patients who had a complete response, 84% were alive at both 1 year and 2 years. For patients who did not get a complete response, 43% were alive at 1 year and 31% at 2 years.

Median survival for all patients was 14 months. Survival was strongly correlated with PET results but not with CT scan results. “Patients who had no response or progressive disease had very poor survival,” Dr. MacManus said. “We performed univariate analysis, looking at the usual prognostic factors, and by far the most important factor was whether or not the patient had a good response on PET scan.”

On multivariate analysis, corrected for stage, ECOG status, and weight loss, PET response remained a powerful predictor of survival, Dr. MacManus said.