The combination of FDG PET/CT and circulating tumor cell (CTC) counts might be a useful tool to monitor response to therapy in breast cancer patients, according to a study published in this month's Journal of Nuclear Medicine.
The predictive significance of 18F-FDG PET/CT findings and CTC counts in patients with bone metastases from breast cancer treated with standard systemic therapy was compared by Naoto T. Ueno, MD, PhD, from the department of breast medical oncology, the University of Texas MD Anderson Cancer Center in Houston, and colleagues.
The study included 55 breast cancer patients with progressive bone-only metastatic disease without visceral metastases starting a new line of systemic therapy and also underwent 18F-FDG PET/CT and CTC counts before and during treatment from December 2004 to May 2008.
Disease status was reassessed by CTC count (greater than or equal to five vs. less than five CTC/7.5 mL of blood) and 18F-FDG PET/CT approximately two to four months after initiation of the new systemic therapy, according to Ueno and colleagues.
The researchers found that the CTC counts at follow-up agreed with the 18F-FDG PET/CT assessment in 78 percent of the 55 evaluable patients. Of the 12 patients with discordant CTC and 18F-FDG PET/CT results, eight (66 percent) had CTCs greater than or equal to five, with no evidence of progressive disease at the time of the 18F-FDG PET/CT study, whereas four (33 percent) had CTCs less than five, with evidence of progressive disease by 18F-FDG PET/CT.
Ueno and colleagues also found that 18F-FDG PET/CT findings and follow-up CTC counts were found to be significantly associated with progression-free survival and overall survival.
In multivariate analysis, the 18F-FDG PET/CT assessment remained as the only predictive factor for progression-free survival, whereas estrogen receptor status was the only predictive factor for overall survival. However, the combination of FDG PET/CT and CTC might be a useful tool to monitor response to therapy in patients without measurable extraosseous disease, especially in patients with elevated CTC at baseline, according to Ueno and colleagues.
The discordance of 18F-FDG PET/CT assessment and CTC count needs to be evaluated in a prospective study to determine the value of 18F-FDG PET/CT and CTC individually and in combination. A prospective study could validate the benefit of these two approaches used separately and in combination in determining prognosis, monitoring response, and establishing bone-dominant disease as a tumor response–measurable disease, concluded Ueno and colleagues.