An emerging picture in cancer biology is that, paradoxically, chemotherapy can actively induce changes that favor cancer progression. These pro-cancer changes can be either inside (intrinsic) or outside (extrinsic) the cancer cells. In this review, we will discuss the extrinsic pro-cancer effect of chemotherapy; that is, the effect of chemotherapy on the non-cancer host cells to promote cancer progression. We will focus on metastasis, and will first discuss recent data from mouse models of breast cancer. Intriguingly, despite reducing the size of primary tumors, chemotherapy changes the tumor microenvironment, resulting in an increased escape of cancer cells into the blood stream. Furthermore, chemotherapry changes the tissue microenvironment at the distant sites, making it more hospitable to cancer cells upon their arrival. We will then discuss the idea and evidence that these devastating pro-metastatic effects of chemotherapy can be explained in the context of stress response. At the end, we will discuss the potential relevance of these mouse data to human breast cancer and their implication on chemotherapy in the clinic.

There is no routine approach to identify patients with gynecologic malignancies at high risk for chemotherapy-resistance. Circulating tumor DNA (ctDNA) tumor fraction (TFx) represents a minimally-invasive approach to tumor profiling, with as yet limited data on utility in gynecologic malignancies. The objective was to investigate the use of ctDNA TFx in a cohort of patients with ovarian and endometrial cancer. Plasma samples from patients with biopsy-proven ovarian or endometrial cancer collected between 4/2018 and 4/2020 were subjected to shallow whole genome sequencing with determination of TFx via ichorCNA package. The association of TFx to continuous and categorical baseline clinicopathologic factors and progression-free survival was assessed. 210 plasma samples from 78 patients with gynecologic cancers were analyzed. Mean TFx for ovarian cancer was 5.5% and endometrial cancer 2.4% and there was no significant difference in TFx among histology either for endometrial or ovarian cancers. Grade was associated with significant difference in ‘sentinel’ TFx among ovarian cancers but not endometrial cancers. ctDNA TFx dynamics over time demonstrated rapid clearance of ctDNA in most patients with ovarian cancer, while endometrial cancer had consistently low TFx. ctDNA TFx is feasible in ovarian and endometrial cancers and may be a valuable important tool for prognostication.