Abstract P6-01-02: Flourine-18-fluorodeoxyglucose positron emission tomography for the evaluation of response to therapy in bone-dominant metastatic breast cancer: Examination in patients enrolled on UPCC 17113
Authors: Lynch MC , Mankoff D , Bradbury AR , Domchek S , Glick JH , Matro J , DeMichele A , Clark AS 
Published: May 2016

Background: Response of bone-only (BO) and bone-dominant (BD) metastatic breast cancer (mBC) to therapy is difficult to assess by conventional imaging. UPCC 17113 is a single institution prospective cohort study evaluating FDG PET at early and conventional follow up intervals, 4 and 12 weeks respectively, in patients with hormone receptor (HR) positive mBC receiving endocrine therapy. The objective of this study is to assess the relationship between changes relative to baseline in standard uptake values (SUV) of specific bone lesions and progression free survival (PFS). We will also explore change in SUV as it relates to overall survival (OS) and skeletal related events (SRE). We present interim results.

Methods: Enrolled patients were ≥18 years with biopsy proven or documented clinically obvious HR-positive BD/BO mBC due to start new endocrine therapy. Any line endocrine therapy was allowed. FDG PET was performed at baseline, 4 and 12 weeks after initiation of new therapy. SUVmax for the 5 most metabolically active osseous lesions, excluding sites previously treated by radiation or surgery, were recorded at baseline, 4- and 12- week time-points. Average index lesion SUVmax (sum SUVmax/#lesions) and % change from baseline were calculated. Decline of ≥30% from baseline was defined as significant.

Results: As of 6/1/2015, 11 patients were enrolled. All patients have completed the 4-week scan and 8 have completed the 12-week scan. Five and 6 out of the 11 patients had BO and BD HR-positive mBC respectively. Detectable changes in SUV from baseline were noted in all patients at both 4 and 12 weeks, with a 37% overall decline in average index lesion SUVmax at 4 weeks. 8 of 11 patients had a ≥30% decline, in SUV at 4 weeks averaging 46%. Five of the 6 patients in this group who completed the 12-week scan had a sustained decline averaging 50% from the baseline. Of note, the average decline between 4 and 12 weeks in this group was only 8%. Despite having an overall decline from baseline of 44%, the sixth patient in this group had an increase between 4 and 12 weeks of 22%. Three of the 11 patients had a &lt;30% decline at 4 weeks with an average decline of 12%. Of the two patients in this group with 12 week scans, both had average increase of 25% from 4 weeks to 12 weeks, and an average overall increase from baseline of 12%.

Conclusions: There are detectable changes in FDG SUV of osseous lesions at 4 and 12 weeks following initiation of endocrine therapy in patients with BO or BD HR positive mBC. Our interim results demonstrate the emergence of 3 groups of patients: (1) those who have a &lt;30% decline at 4 weeks and increase of SUV at 12 weeks, (2) those who have a ≥30% decline in SUV at 4 weeks with sustained decline at 12 weeks, and (3) those who have a ≥30% reduction in SUV at 4 weeks but who do not have a sustained decline at 12 weeks. These interim results suggest that early FDG PET/CT may provide information on mBC response to endocrine therapy and insight into timing of response and progression. As more patients are enrolled and complete the studies, clearer patterns will emerge which will be correlated with PFS, OS and SRE.

Citation Format: Lynch MC, Mankoff D, Bradbury AR, Domchek S, Glick JH, Matro J, DeMichele A, Clark AS. Flourine-18-fluorodeoxyglucose positron emission tomography for the evaluation of response to therapy in bone-dominant metastatic breast cancer: Examination in patients enrolled on UPCC 17113. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-01-02.