Biomarkers that are predictive of clinical benefit in Trop-2-expressing triple-negative breast cancer

Reviewed by Emily Henderson, B.Sc.Nov 3 2020

Oncotarget recently published "Predictive biomarkers for sacituzumab govitecan efficacy in Trop-2-expressing triple-negative breast cancer" which reported that the authors investigated whether Trop-2-expression and homologous recombination repair of SN-38-mediated double-strand DNA breaks play a role in the sensitivity of triple-negative breast cancer to SG.

Further, two Trop-2-transfectants of MDA-MB-231, C13, and C39, were treated in mice with SG to determine whether increasing Trop-2 expression improves SG efficacy.

SG mediated >2-fold increase in Rad51 in MDA-MB-231 but had no effect in SK-MES-1 or HCC1806, resulting in lower levels of dsDNA breaks in MDA-MB-231. SG and saline produced similar effects in parental MDA-MB-231 tumor-bearing mice.

However, in mice bearing higher Trop-2-expressing C13 and C39 tumors after Trop-2 transfection, SG provided a significant survival benefit, even compared to irinotecan.

These results suggest that SG could provide better clinical benefit than irinotecan in patients with HRR-proficient tumors expressing high levels of Trop-2, as well as to patients with HRR-deficient tumors expressing low/moderate levels of Trop-2.

In recent years, there has been an increased focus on personalized cancer therapy."

Dr. Thomas M. Cardillo from Immunomedics, Inc

SG demonstrated significant clinical benefit across a range of solid tumors, including metastatic TNBC, hormone-positive breast cancer, small-cell lung cancer, non-small-cell lung cancer, and metastatic urothelial carcinomas.

It remains unclear from these results whether the overriding mechanism for SG sensitivity in these various tumor models is Trop-2 expression or defective HRR pathways, or their combination.

Herein, the Oncotarget authors examined the HRR response in MDA-MB-231, being unresponsive to SG, including upregulation of Rad51 and levels of dsDNA breaks mediated by SG exposure, and compared it to that of SG-sensitive tumor lines to elucidate the role that this pathway plays in protecting cells from SG-mediated dsDNA breaks.

Additionally, MDA-MB-231 cells transfected to express higher levels of Trop-2 were assessed in vivo for SG antitumor effects in comparison to parental tumors with low Trop-2 expression.

However, this does not rule out SG being active in tumors with low Trop-2 expression and deficiencies in HRR.

The Cardillo Research Team concluded in their Oncotarget Research Paper that, these data strongly support the hypothesis that as a biomarker, high surface Trop-2 expression on a patient's tumor may be predictive of a positive clinical outcome for SG therapy.

Further, there are secondary biomarkers that may need to be considered for those patients with low/moderate Trop-2 expression or those with high Trop-2 expression that failed previous irinotecan therapy for reasons other than acquired resistance.

Moreover, while high expression of Trop-2 was found to be a primary biomarker for SG efficacy, it should not be a limiting factor, because other secondary biomarkers coupled with Trop-2 expression may likewise be predictive of clinical benefit.

For these reasons, future clinical trials will need to comprehensively examine potential biomarkers, in addition to Trop-2 expression, to generate a profile that will better identify those patients likely to benefit from SG therapy.