Assessment of bone metastases by bone scan after treatment with zoledronic acid in patients with breast cancer

Objectives To evaluate the therapy effects on bone scintigraphy (BS) in patients treated by zoledronic acid (ZA).

Methods In sequential 5885 cases underwent BS between January 2008 and December 2011, 11 patients of 25 intervals with bone-only metastatic disease without visceral metastases , and with significant increase of tumor marker (TM) were included in this study. All 11 patients were female and affected by breast cancer, ranging from 36 to 74 years (mean age ± SD: 60±9.9 years). CT and BS were independently analyzed by three readers. The effect of therapy was evaluated as follows: CR, when no bone metastasis was visible; PR, when a decrease in the number, extent or the intensity of the lesion could be detected; SD, when no or slight change in the number, extent or the intensity of bone metastases could be observed; PD, when new bone lesion or enlargement of the bone metastases were visualized. In TM evaluation, PD was defined as >20% increase, PR was >20% decrease, SD was within 20% change, and CR was defined as decrease below the cut-off level. Evaluation of therapeutic effect by BS and CT during the course of treatment was compared with the changes in TM value.

Results The concordance rate between TM and BS was 76%, 80% and 76%, CT was 52%, 48%, 40%, BS and CT combined was 64%, 52% and 60% in reader 1, 2 and 3 respectively. Significant difference was observed in reader 2 and 3 between CT and BS. Percentage of interobserver agreement between reader 1 and 2, reader 1 and 3, and reader 2 and 3 was 84%, 80% and 88% (κ=0.648, 0.561 and 0.766) for BS, 52%, 56%, and 60% (κ=0.180, 0.278 and 0.282) for CT, 52%, 60%, and 56% (κ=0.215, 0.282 and 0.232) for CT and BS combined respectively.

Conclusions BS is an appropriate modality to monitor the response to bone metastases in patients treated with ZA, although possibility of misdiagnose tumor response as stable or progression were indicated.