Multi-step evolution characterizes the carcinogenesis of GI malignancies, where the disease progresses through the accrual of genetic mutations, co-option of multiple host cellular factors and the acquisition of increasingly aggressive pathological features. Ensuing cancer complexity and plasticity are challenges for therapeutic approaches. On the other hand, disease inception is often triggered by a defined oncogenic event, which leads to escalating effects on gene expression, cellular metabolism, chromatin organization and ultimately cell identity. Decoding this molecular cascade of events is crucial to design strategies for early diagnosis as well as to tackle tumor onset. To this aim, the in vitro culture of non-transformed epithelial cells represents a major technical challenge. Genetic studies, combined with lineage-tracing experiments demonstrated that pancreatic cancerous lesions originate from acinar cells, a specialized cell type in the pancreatic epithelium, following mutations of the KRAS oncogene. Ex vivo culture of pancreatic acinar cells has allowed the identification of early mutant KRAS-driven alterations. Primary acinar cells survive in vitro in organoid-like 3D spheroids, which can recapitulate histological and molecular features of disease initiation. Here, we will discuss the isolation and culture of primary mouse pancreatic acinar cells, providing and historical and technical perspective. Impact for pancreatic cancer research will also be debated; in particular we will dissect the role of KRAS signaling in driving oncogenic transformation and highlight differences with canonical 2D culture of established cancer cell lines.