Background: Low hematologic counts are a common, costly side effect of chemotherapy. This observational study examines rates and associated cost to treat. Methods: Data on adverse events (AEs) were extracted from the clinical Flatiron Health database for mPC patients (pts) from 01/2014-01/2019. Anemia, neutropenia, and lymphopenia occurrence was assessed via diagnosis codes and structured lab data. Costs due to AEs were derived from a claims analysis of mPC pts from 2013-2017 in Medicare Limited Data Set claims. Mean adjusted incremental costs (ICs) were estimated by comparing 30-day costs of pts with and without AEs, with controls selected among pts without AEs with the same regimen and line of therapy, when at least 80 cases/controls were identified. Results: 4592 treated mPC pts were identified (median age at diagnosis: 68y, IQR: 61 – 75). 1138 pts were treated with FOLFIRINOX (FFX) in first-line (1L), 2295 pts with 1L gemcitabine plus nab-paclitaxel (gem-nab), 218 pts with second-line (2L) FOLFOX, 56 pts with 2L FOLFIRI, and 178 pts with 2L liposomal irinotecan (nal-IRI) based therapy. Observed rates of anemia and neutropenia are shown in the table below. Lymphopenia rates were similar across regimens and ICs were not statistically significant. ICs for patients with any grade anemia were $3864, $3818, $3536, $3978, and $2963 for FFX, gem-nab, FOLFOX, FOLFIRI, and nal-IRI treated pts, respectively. ICs for pts with any grade neutropenia were $2382 for FFX, $2440 for gem-nab, $2688 for FOLFOX, $3551 for FOLFIRI and $2307 for nal-IRI. Conclusions: Any grade anemia ICs ranged from $2963 [$1544, $4400] (nal-IRI) to $3978 [$2241, $5817] (FOLFIRI), and any grade neutropenia ICs ranged from $2307 [$703, $4313] (nal-IRI) to $3551 [$1227, $6039] (FOLFIRI). Pts treated with nal-IRI had similar any grade AE rates but lower ICs, which suggest lower severity of AEs. These results are consistent with Flatiron Health’s lower rates of grades 3+ neutropenia and anemia.