Can positron emission tomography predict the outcomes of patients with high risk rectal cancer?

This study investigated the use of ¹⁸F-2-fluoro-2-deoxy-D-glucose positron emission tomography (¹⁸F-FDG-PET) to follow-up during treatment and predict the outcomes of patients with high-risk localized rectal cancer. Researchers suggested that this method can be very useful to assess the tumor before the surgery and predict response to treatment.

Treatments before surgery have improved greatly the outcomes of patients with locally advanced rectal cancer (spread to the lymph nodes). Moreover, the negative side effects of radical surgery in the quality of life of these patients have led to the use of less invasive methods.

A complete tumor response (shrinkage) after treatment is often not followed by surgery. These patients are clinically followed-up under the strategy of “watch and wait”. However, the follow-up methods might be of only limited effectiveness. ¹⁸F-FDG-PET consists of injecting a small amount of a radioactive drug (¹⁸F-FDG) into the body followed by a full body scan. This drug will show any metastasis (spread cancer) present in the body. Prior studies showed that this method is associated with early treatment response prediction. Therefore, patients will follow with adequate treatment.

The ¹⁸F-FDG-PET effectiveness in the follow-up of patients with high-risk rectal cancer treated with bevacizumab (Avastin) is still not clear.

This study included 61 patients treated with radiation therapy, chemotherapy, and bevacizumab. ¹⁸F-FDG-PET was performed at the start of the study, 11 days after the beginning of treatment and before surgery. Tumor response, progression-free survival (PFS; time from treatment to cancer progression) and overall and cancer-specific survival (CSS) were assessed.

¹⁸F-FDG-PET was able to find a difference between the initial scan and the following scans regarding the detection of early metastasis.  

After an average follow-up of 98 months, good treatment responders showed a 10-year PFS of 89.3% and a CSS of 92.9%. The poorer responders had a 10-year PFS 63.6% and a CSS of 72.6%.

This study concluded that ¹⁸F-FDG-PET is a useful tool in the before surgery in the follow-up of patients with high-risk localized rectal cancer.

This study included a very small number of participants. Larger studies are needed.