PET scans accurately detect a breast tumor's response to chemotherapy

Researchers in Australia have shown that positron emission tomography (PET) that uses a radioactive sugar molecule is more useful than mammography and ultrasound in predicting a breast tumour's response to chemotherapy and, therefore, the patient's ultimate likelihood of survival.

In research presented at the European Cancer Conference (ECCO 14) in Barcelona, Dr Vinod Ganju reported that when the scanning procedure was used to measure the accumulation of radioactive glucose fluorodeoxyglucose (FDG) in tumour tissue from patients with locally-advanced breast cancer before and after preoperative chemotherapy, women who had the highest accumulation at the beginning and who then had the highest percentage drop in accumulation after four cycles of chemotherapy were more likely to have a complete response to their treatment i.e. no tumour cells remaining in the final tumour resection specimen. However, measurements taken using mammography or ultrasound were not able to predict a pathological response accurately.

FDG-PET works by injecting a sugar molecule (FDG), tagged with a radioactive tracer, into the patient. The molecule is metabolically active and concentrates in tumour tissues where it emits energy that PET scanning can detect. PET measures the “standard uptake values” (SUVs), in other words, how much FDG has accumulated in the tumour. If the SUVs drop after chemotherapy, this shows that there are fewer, or no, cancer cells available where the FDG can accumulate. This study suggests that tumours with high initial SUVs seem to be more sensitive to chemotherapy, thereby giving a better chance of achieving a reduction or complete removal of the cancer.

Dr Ganju, a medical oncologist for Monash Oncology Research Institute (MORI) and Monash Breast Cancer Research Consortium, Monash Medical Centre, Melbourne, Australia, said: “In our study, we were able to show that patients who had higher baseline SUVs and a greater reduction in SUV at the second PET scan, were more likely to respond to the chemotherapy and achieve a complete pathological response. Patients who achieve a complete pathological response are more likely to survive and have a better prognosis.”

The researchers recruited 47 women with locally advanced breast cancer to their study, and they were able to evaluate data from 44 of these women. The patients were randomly assigned to receive either fluorouracil, epirubicin, cyclophosphamide (FEC) followed by docetaxel, or docetaxel followed by FEC. They were assessed at the start by PET scans, physical examination, mammography, ultrasound and tumour biopsy, and again after four cycles of chemotherapy. The initial SUVs and the percentage reduction in SUVs after chemotherapy were correlated to pathological response (complete, partial or no response) as assessed by examination of biopsy samples.

Nine women had a complete pathological response (pCR), 15 had a partial response (pPR) and 20 less than optimal pathological response (NR) to chemotherapy. Women who had a pCR were significantly more likely to have higher SUVs before chemotherapy than NR women (an average of 9.7 versus 6.4 on the SUV measurement scale). The percentage reduction in SUVs after chemotherapy was also significant, with SUVs in pCR women reducing by an average of 83.3 percent compared to 50.4 percent in NR women.

Dr Ganju said: “This study shows that women with high baseline SUVs and a higher percentage reduction of SUVs after four cycles of chemotherapy are more likely to achieve a pathological complete response to neoadjuvant chemotherapy. FDG-PET appears to be an important addition to conventional imaging of women with breast cancer and may contribute significantly to a more individualised management of their disease. Currently, all patients receive the same chemotherapy regardless of their tumour characteristics. It would be very valuable to target therapies according to baseline tumour characteristics. This could spare the patient unnecessary on-going chemotherapy, or enable them to switch to a different therapy if the first was found to be ineffective.”

PET technology is advancing all the time. “Different tracer molecules other than glucose are available for PET studies. These may prove even more useful in the future, but most are still in the experimental stages,” concluded Dr Ganju. The group is also currently correlating the results from this study with the genetic profile of the tumours.

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