Abstract 294: Upfront identification of chemoresistance in locally advanced breast cancer using 99m Tc Tetrofosmin scan prior to definitive surgery

Abstract

Abstract Background: Locally advanced breast cancer (LABC) is the commonest stage of presentation (∼50-60%) in India. Neoadjuvant chemotherapy (NACT) is the standard method of treatment. However, only about ∼30% of patients have complete response to first line NACT. Thus, it is important to identify the subset of LABC that are chemoresistant early in the course of treatment. PET scan has been used in the West to identify chemoresistance in LABC. However, PET scan facility is not available in most centres in India and is expensive. Thus, there is need for a cost effective investigation which is accurate in identifying chemoresitiancet in Indian settings early in the course of treatment. Aim: To evaluate the role of Tc 99m-Tetrofosmin scan in distinguishing chemo sensitive from chemo resistant LABC prior to institution of NACT. Patients & Methods: Sixty five female patients with LABC (T3N0/N1; T4bN0/N1) were included in this study. The study was performed according to the approved guidelines of institutional ethical committee. Informed consent was obtained from all patients. Patients not fit to receive chemotherapy, who have received some form of NACT before presentation to us, or refusing enrollment were excluded from the study. 99m Tc Tetrofosmin scintimammography was performed in all the patients. 3 cycles of Cyclophosphomide, Adriamycin & 5-Fluro-uracil were administered at 3 week intervals.Response was evaluated 2 weeks after the 3rd cycle by clinical evaluation, 99m Tc Tetrofosmin Scintimammography and histopathology. Results: A ROC (Receiver Operating Characteristic) curve was plotted (using SAS 8.0 software) for the T/B (tumor background) ratio and pathological response. Area under the curve was found to be 84% with a confidence interval between 73%-95%. Using this curve, a cut off value of 2.55(at which the maximum accuracy of 84%) was chosen to characterize the chemo sensitivity of the tumors between complete and less than complete response. When the T/B ratio >2.55, 18 patients had no tumor at histopathology and 12 patients had less than CR.Even among these 12 patients, the tumor regressed significantly in 6 patients (very good partial response) and >50% in 6 other patients. On the other hand, when the T/B ratio was <2.55, only 1 patient had complete regression of the tumor and 30 patients had tumor at histopathology. Of these 30 patients, the tumor reduction was <50% in 9(15%) patients,>50% in 14(23%) patients and >75% in 7(12%) patients. The sensitivity, specificity and accuracy of 99m Tc Tetrofosmin Scintimammography in predicting chemo sensitivity to Doxorubicin based chemo therapy was 95%, 72%and 84% respectively. Conclusion: Tc99 tetrofosmin can accurately identify chemo sensitive tumors and predict response to NACT in LABC. Its low, cost, high accuracy and wider availability in developing nations makes it an attractive option in management of LABC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 294. doi:10.1158/1538-7445.AM2011-294