Purpose: Monitoring of response to neoadjuvant chemotherapy (NCT) is important for optimal management of patients with breast cancer. (99m)Tc-3PRGD2 SPECT is a newly developed imaging modality for evaluating tumor vascular status. In this study, we investigated the application of (99m)Tc-3PRGD2 SPECT in evaluating therapy response to NCT in patients with stage II or III breast cancer.
Methods: Thirty-three patients were scheduled to undergo (99m)Tc-3PRGD2 SPECT at baseline, after the first and second cycle of NCT. Four patients had extremely low (99m)Tc-3PRGD2 uptake at baseline, and were not included in the subsequent studies. Changes in tumor to nontumor (T/N) ratio were compared with pathological tumor responses classified using the residual cancer burden system. Receiver operator characteristic analysis was used to compare the power to identify responders between the end of the first and the end of the second cycle of NCT. The impact of breast cancer subtype on (99m)Tc-3PRGD2 uptake was evaluated. The correlation between (99m)Tc-3PRGD2 uptake and pathological tumor response was also evaluated in each breast cancer subtype.
Results: Surgery was performed after four cycles of NCT and pathological analysis revealed 18 responders and 15 nonresponders. In patients with clearly visible (99m)Tc-3PRGD2 uptake at baseline, the sensitivity, specificity, and negative predictive value of (99m)Tc-3PRGD2 SPECT were 86.7 %, 85.7 % and 86.7 % after the first cycle of NCT, and 92.9 %, 93.3 % and 93.3 % after the second cycle, respectively. Among these patients, the HER-2-positive group demonstrated both higher T/N ratios and a greater change in T/N ratio than patients with other breast cancer subtypes (P < 0.05). A strong correlation was found between changes in T/N ratio and pathological tumor response in the HER-2-positive group (P < 0.03).
Conclusion: (99m)Tc-3PRGD2 SPECT seems to be useful for determining the pathological tumor response in patients with stage II or III breast cancer undergoing NCT, especially those with the HER-2-positive subtype.