Highlights
- •Key Finding: In early stage ER/PR+ HER2- breast cancers treated with neoadjuvant radiation therapy, the percent volume of tumor remaining on post-SABR MRI compared to baseline correlates with surgical pathology percent tumor bed cellularity.
- •Importance: This finding allows pre-surgical assessment of neoadjuvant radiotherapy response in these ER/PR+ HER2- tumors for which pathologic complete response is rare.
Abstract
Objective
This study evaluates breast MRI response of ER/PR+ HER2- breast tumors to pre-operative
SABR with pathologic response correlation.
Methods
Women enrolled in a phase 2 single institution trial of SABR for ER/PR+ HER2- breast
cancer were retrospectively evaluated for radiologic-pathologic correlation of tumor
response. These patients underwent baseline breast MRI, SABR (28.5 Gy in 3 fractions),
follow-up MRI 5 to 6 weeks post-SABR, and lumpectomy. Tumor size and BI-RADS descriptors
on pre and post-SABR breast MRIs were compared to determine correlation with surgical
specimen % tumor cellularity (%TC). Reported MRI tumor dimensions were used to calculate
percent cubic volume remaining (%VR). Partial MRI response was defined as a BI-RADs
descriptor change or %VR ≤ 70%, while partial pathologic response (pPR) was defined
as %TC ≤ 70%.
Results
Nineteen patients completed the trial, and %TC ranged 10% to 80%. For BI-RADS descriptor
analysis, 12 of 19 (63%) showed change in lesion or kinetic enhancement descriptors
post-SABR. This was associated with lower %TC (29% vs. 47%, P = .042). BI-RADS descriptor change analysis also demonstrated high PPV (100%) and
specificity (100%) for predicting pPR to treatment (sensitivity 71%, accuracy 74%),
but low NPV (29%). MRI %VR demonstrated strong linear correlation with %TC (R = 0.70,
P < .001, Pearson's Correlation) and high accuracy (89%) for predicting pPR (sensitivity
88%, specificity 100%, PPV 100%, and NPV 50%).
Conclusion
Evaluating breast cancer response on MRI using %VR after pre-operative SABR treatment
can help identify patients benefiting the most from neoadjuvant radiation treatment
of their ER/PR+ HER2- tumors, a group in which pCR to neoadjuvant therapy is rare.
Keywords
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Article info
Publication history
Published online: July 19, 2021
Accepted:
June 28,
2021
Received in revised form:
April 29,
2021
Received:
October 28,
2020
Identification
Copyright
© 2021 Elsevier Inc. All rights reserved.
