ASCO GU 2018: Targeting Bacteroides in the Stool Microbiome and Response to Treatment in Metastatic Renal Cell Carcinoma

San Francisco, CA ( Response to VEGF-TKI therapy has been correlated with the ability to tolerate the standard dose of treatment. The most common side effect leading to dose reduction or treatment discontinuation is TKI associated diarrhea. Pal et al. demonstrated that stool Bacteroides spp. level correlated with the presence and severity of diarrhea in metastatic renal cell carcinoma (mRCC) patients treated with VEGF-TKIs. The authors of the above abstract attempt to correlate the use and duration of antibiotics targeting stool Bacteroides spp. with survival outcomes with the hypothesis that reduction in TKI-induced diarrhea would lead to increased tolerability of standard doses and as a result improve survival outcomes measures. 

The authors performed a retrospective review of 145 patients undergoing VEGF-TKI therapy for intermediate and poor risk MSKCC risk criteria mRCC. The group was then stratified into three groups: No antibiotic (96 pts), Antibiotic with Bacteroides spp. coverage (17 pts) and antibiotic with non- Bacteroides spp. coverage. There was no difference in the baseline clinicopathological characteristics between the three groups.  The patients who were treated with antibiotic with Bacteroides ssp. coverage has a longer progression-free survival (PFS) interval of 18 months compared to 8 months in those who did not receive antibiotics (p=0.059). The PFS interval for those who received antibiotics with non-Bacteroides spp. coverage was similar to the non-antibiotic group (9 months). In those treated with antibiotics, the median number of treatment days 7 (IQR 1.3-10 days). When compared to those with no antibiotics, duration of Bacteroides ssp. coverage resulted in an 8% improvement in PFS for each additional day on antibiotic coverage. 

The study presented has serval limitations, the most important it’s the limited sample size (17 pts) of patients treated with antibiotics covering Bacteroides spp. The authors fail to show a causal association between antibiotic treatment and diarrhea improvement since the severity of diarrhea was not able to be extracted from the medical record. Further work to elucidate this hypothesis is needed not only for the improvement in cancer response but also for the gain in quality of life. 

Presented by: Camryn Froerer, PharmD Candidate, University of Utah Huntsman Cancer Institute, Salt Lake City, UT

Written by: Andres F. Correa, MD, Fox Chase Cancer Center, Philadelphia, PA at the 2018 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, February 8-10, 2018 - San Francisco, CA