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Metastatic pancreatic cancer (PC) is an aggressive malignancy, with most patients deriving benefit only from first-line chemotherapy. Increasingly, the recommended treatment for those with a germline mutation in a gene involved in homologous recombination repair is with a platinum drug followed by a poly (ADP-ribose) polymerase (poly adenosine phosphate-ribose polymerase [PARP]) inhibitor. Yet, this is based largely on studies of BRCA1/2or PALB2mutated PC. We present the case of a 44-year-old woman with ATM-mutated PC who achieved stable disease as the best response to first-line fluorouracil, leucovorin, irinotecan, and oxaliplatin, followed by progression on a PARP inhibitor. In the setting of jaundice, painful hepatomegaly, and a declining performance status, she experienced rapid disease regression with the nonplatinum regimen, gemcitabine plus nab-paclitaxel. Both physical stigmata and abnormal laboratory values resolved, imaging studies showed a reduction in metastases and her performance status returned to normal. Measurement of circulating tumor DNA for KRAS G12Rby digital droplet polymerase chain reaction confirmed a deep molecular response. This case highlights that first-line treatment with a platinum-containing regimen followed by PARP inhibition may not be the best choice for individuals with ATM-mutated pancreatic cancer. Additional predictors of treatment response are needed in this setting.