K-Ras4B is a highly oncogenic Ras isoform and is the only isoform associated with initiation of adenocarcinomas. Mechanistic insight into why and how K-Ras4B mediates ductal adenocarcinomas, particularly of the pancreas, is vastly important for its therapeutics. The current review points out the overlooked but critical role of calmodulin (CaM) which selectively binds to GTP-bound K-Ras4B; but not to its isoforms. Cell proliferation and growth require the MAPK (Ras/Raf/MEK/ERK) and PI3K/Akt signaling pathways. We propose how Ca2+/CaM promotes PI3K/Akt signaling and how Ca2+/CaM involvement explains enigmatic observations like the elevated calcium levels in adenocarcinomas. We hypothesize that CaM recruits and activates PI3K at the membrane, and that this is the likely reason for Ca2+/CaM-dependence in adenocarcinomas. CaM contributes to initiation and progression of many ductal cancers (e.g., pancreatic, colorectal, lung) via both PI3Kα/Akt and Raf/MEK/ERK pathways. Therefore, blocking the K-Ras/MAPK pathway and CaM/PI3Kα binding in a K-Ras4B/CaM/PI3Kα heterotrimeric complex has promising clinical potential as an adenocarcinoma-specific therapeutic strategy.