Abstract P2-02-16: Use of cell-free circulating RNA and expression of PD-L1 and HER2 in plasma to monitor and predict clinical response in metastatic breast cancer patients
Authors: Castrellon AB , Velez M , Raez LE , Danenberg K , Rabizadeh S , Usher J , Jaimes Y , Hunis B , Bittencourt AC , Milillo A , Blaya M , Habaue C , Danenberg PV 
Published: February 2018

Background: In addition to traditional radiology tests, cell-free circulating tumor RNA (cfRNA) extracted from plasma of cancer patients (pts) provides a means of evaluating tumor response, but based on molecular changes in the tumor. Measuring dynamic changes in gene expression and levels of total cfRNA (per ml of plasma) in metastatic patients has shown great potential for evaluating disease status and predicting outcome to anti-tumoral therapy in advance of imaging. Though checkpoint inhibitors have not been assessed widely in breast cancer, TNBC has shown mild responses to pembrozilumab and atezolizumab, with significantly better responses in pts with detectable PD-L1 expression.

Methods: Blood was drawn from pts at approximately 6-week intervals under various therapies and CT scans were performed at approximately 3-month intervals. CfRNA was extracted from the resulting plasma and reverse transcribed with random hexamers to cDNA. Levels of cfRNA were quantitated by RT-qPCR and correlated with pt response (PR/SD/PD), as determined by CT scans. Levels of gene expression in cfRNA (including PD-L1 and HER2) were monitored in pts across blood draws.

Results: A total of 28 breast cancer pts were enrolled in a 1-year clinical study. Of pts, 39% (11/28) were Caucasian and 36% (10/28) Hispanic. 19 pts completed the first two cycles of therapy: 2 pts had PR and showed no change (NC) or decrease (DEC) in levels of cfRNA, 11 pts achieved SD with 8 showing DEC or NC in cfRNA levels, and 6 pts had PD and all underwent increases (INC) in cfRNA levels (median increase: 788 ng/mL plasma) which correlated with progressive disease status. Of pts with SD/PR, 4 showed either an emergence or significant increase in PD-L1 expression across blood draws (3.7-98 ct); of PD pts, 1 showed a significant emergence of PD-L1 expression (12.5 ct) across blood draws. 3/5 of these PD-L1 expressing pts were being treated with an everolimus combination; the emergence or increase of PD-L1 in response to this therapy suggests use of checkpoint inhibitors as an option for these pts. In response to therapy, 3 of 5 pts had PD-L1 cfRNA levels above levels predictive of response to nivolumab in lung cancer pts. In the only pt with hyperexpressed HER2, the disappearance of HER2 cfRNA matched positive response (PR) to treatment with trastuzumab. PD-L1 decreased concomitantly for this pt.

Conclusion: We found a strong correlation between clinical responses and changes in plasma levels of ctRNA in breast cancer (84%). Most of these were documented several weeks before imaging was done. Levels of PD-L1 and HER2 expression in plasma can also be used to monitor pt response to specific therapies. The emergence of PD-L1 expression in response to various therapies in breast cancer may confer sensitivity to checkpoint inhibitor therapy.

Citation Format: Castrellon AB, Velez M, Raez LE, Danenberg K, Rabizadeh S, Usher J, Jaimes Y, Hunis B, Bittencourt AC, Milillo A, Blaya M, Habaue C, Danenberg PV. Use of cell-free circulating RNA and expression of PD-L1 and HER2 in plasma to monitor and predict clinical response in metastatic breast cancer patients [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-02-16.