Background: Standard of care treatment for pancreatic adenocarcinoma (PDAC) includes FOLFIRINOX or gemcitabine with nab-paclitaxel used in either the front-line or 2^nd line treatment setting. There is no consensus for 3^rd line treatment for this cohort of poor prognosis patients with clinical trials being the only viable option. We evaluated a cell viability assay using cultures of circulating tumor and invasive cells (CTICs) to identify effective 3^rdline PDAC treatment options. Methods: CTICs were isolated from peripheral blood samples of 17 PDAC patients who previously had received one of the two standard of care regimens using an immunomagnetic separation for EPCAM epitope Ber-EP4 and cultured in enriched DMEM-F12 medium. After 14 days, seven chemotherapeutics (gemcitabine (G), oxaliplatin (O), fluorouracil (F), irinotecan (I), mitomycin C (M), cisplatin (C) and paclitaxel (P)) were added to the cultures and response to treatment was measured 48 hr. after treatment by immunofluorescence using a live-cell resazurin assay. Response to treatment was determined by a reduction of fluorescence in the treated cultures compared to control and the mean florescence (Fm) was calculated for each chemotherapeutic. A one-sample t-test was used to measure the variance between Fm control and treated samples. (p-value <0.005). Sensitivity to treatment was determined using linear regression based on Fm values and the sensitivity of each chemotherapeutic was interpolated from a standard curve (range 1.0-5.0, sensitive <2, intermediate 2-3, resistant >3). Results: m (Fm=1.6) demonstrated the most effective treatment option with marked resistance to treatment for G, I, P and O. (Fm=3.4, 3.7, 3.4 and 3.7). Intermediate response was observed for F and C (Fm=2.8 and 2.8). Patient treatment response to m will be described. Conclusions: CTICs can be routinely isolated and cultured for cell viability assays. m based regimens with C and F should be considered for 3^rd line PDAC patients.