Whole-body PET/CT scans take on colon cancer, other new challenges

A whole-body PET/CT scan can be used to stage and further pinpoint cancers spotted on optical colonoscopy, a research team for Essen University reported Monday. The team also reported that PET/CT scans may be useful in restaging recurrent breast cancer.

The papers were among several evaluating the use of PET/CT in advanced applications. Generally, they reported good results. One study that evaluated whole-body MR and whole-body PET/CT for imaging lymph node and distant metastases secondary to melanoma gave both modalities relatively low marks for sensitivity, however, resulting from their inability to spot small lesions.

The whole-body colonoscopy study included 14 patients and was designed to evaluate whether the PET/CT scan could be successfully integrated with a dedicated CT and an optical colonoscopy exam. The researchers concluded that it could and that it allows accurate TNM staging in patients with colorectal cancer.

PET/CT colonography detected 18 of 19 lesions identified by conventional colonoscopy, missing only one flat lesion. Six extracolonic tumor sites were also detected with the PET/CT scan. Based on the imaging findings, 11 patients were treated surgically, and three by chemotherapy. Histologic data showed that imaging revealed correct T-stage in eight of the 11 patients and correct N-stage in nine patients.

The breast cancer study evaluated 58 patients suspected of recurrent breast cancer. All underwent whole-body PET/CT scans with FDG. Correct TNM tumor stage identification varied with modality:

• 93% with PET/CT

• 90% with PET and CT scans reviewed side by side

• 84% with CT alone

• 79% with PET alone

The study of malignant melanoma patients was also conducted by Essen University. It included data from 31 patients who had whole-body contrast MR scans and whole-body FDG-PET/CT scans. PET/CT had a sensitivity of 50% and a specificity of 100% for N-stage cancers, compared with 33.3% and 100%, respectively, for MR. PET/CT had a sensitivity of 37.5% and a specificity of 95.4% for M-stage cancers, compared with 12.5% and 95.5%, respectively, for MR.

An analysis of the data showed that the sensitivity figures were pulled down by missed cancers 7 mm or smaller, said Dr. Florian Vogt, who presented the data.