Correlation on metabolic complete response on positron emission tomography and pathological complete response in patients with breast cancer after neoadjuvant chemotherapy

Purpose: The use of neoadjuvant chemotherapy in treating breast cancer has expanded in recent years. There was increased interest in using positron emission tomography (PET) for the evaluation of treatment response. We aimed to study the accuracy of metabolic complete response (mCR) on PET scan in predicting pathological complete response (pCR) after neoadjuvant treatment.

Methods and results: Between January 1, 2014 and June 30, 2019, 356 consecutive patients who completed neoadjuvant treatment underwent PET scan before surgery. 207 patients (58.1%) achieved mCR and 128 patients (36.0%) achieved pathologic CR. Among mCR patients, 101 (48.8%) had pCR. Among pCR patients, 27 (21%) did not achieve mCR on PET. The overall sensitivity of predicting pCR with mCR was 78.9% and specificity of 53.5%. The overall accuracy was 0.691 by area under the receiver operating characteristic curve (AUC). Analysis using mCR to predict breast/axilla pCR had a sensitivity of 76.2%/67.9%, specificity of 54%/62.1%, and AUC of 0.682/0.675, respectively. Sensitivity and specificity were highest among HR-/HER2+ (87.1% and 57.1%), followed by HR+/HER2- (85% and 59.6%) and triple negative (82.1% and 54.1%) and the lowest were HR+/HER2+ (triple positive) (69.4% and 40.3%). There was little difference in sensitivity and specificity among the high and low Ki67 proliferation index (78.3% vs. 75% and 52.1% vs. 62.5%).

Conclusion: PET was useful in evaluation of tumor response to neoadjuvant chemotherapy especially in the HR-HER2+ subtype. However, its accuracy was not high enough to replace surgery.