Background: The use of alternating chemotherapy regimens in cancer therapy may 1)lessen toxicity 2) slow emergence of resistant cancer biology thus improving outcomes and 3) provide a broader platform for the addition of other (non)chemotherapeutic (CT) agents to the base regimen. This strategy using alternating G/A and FOLFIRI in MPC was first tested in the SEENA-1 trial ( Picozzi et.al. GI Cancer Symposium 2017). We sought to extend these observations at our institution. Methods: Eligible patients (pts) had the following characteristics: 1) bx proven de novo MPC, 2) no prior CT , 3) ECOG PS 0/1 , and 4) bidimensionally measurable disease. Treatment (Rx) consisted of 1) gemcitabine 1000mg/m² and nab- paclitaxel 125 mg/²d 1,(8),15 alternating every 8 weeks (2 cycles) with 5-FU. Pts were radiographically restaged every 8 weeks. Rx was continued for up to 48 weeks, at which time additional therapy was given per physician/patient decision. Results: From 10/1/2015 thru 1/1/2018, 40 pts were treated via this method. Pt characteristics included median age 67, ECOG PS 0/1, 58%/42%. Frequent metastatic disease sites included liver 78%, peritoneum 45%, lung 23%. 33 pts have completed Rx , 7 pts remain on Rx. Toxicity generally was less than typical in either individual regimen (e.g. no ≥ grade 3 neuropathy or diarrhea was seen). Of pts completing Rx, median number of cycles given was 8; 13/33 pts (39%) completed all 48 weeks intended Rx. Disease control rate in 34 currently evaluable pts at 16 weeks was 85% (47% PR/38% SD/15% PD). As of 1/1/2018, median f/u is 9.5 mo; 21/37 evaluable pts remain alive (3 transferred care). PFS is 9.2 mo (95% CI 5.9-10.6 mo), 1-year OS is 61%, median OS is 16.3 mo (95% CI 9.7 mo-NR). Conclusions: 1) The above alternating regimen approach in MPC showed promising results with respect to toxicity and response. 2) This approach offers a platform for further regimen development in MPC. 3) We continue to accrue experience with this regimen.