The scientific community has become more enthusiastic about ketogenic diet (KD) to improve the outcomes in medical conditions, including cancer by exploiting the reprogramed metabolism of cancer cells, making the diet a promising candidate as an adjuvant cancer therapy. From this perspective, the aim of this study was to provide a broad overview covering the therapeutic effects, evaluating the clinical evidence of clinical studies underlying the implementation of the KD in the context of cancer treatment and prognosis. A scoping literature search between the years 1990 and 2023 was carried out by using PRISMA guidelines and searching through different databases of the clinical studies supporting the effectiveness and benefits of KD in various carcinomas that could provide findings of evidence on the prognosis and clinical outcomes of cancer treatment. A total of 23 cancer-related publications were included, 12 of which focused on brain cancer particularly glioblastoma multiforme (GBM), 4 on both breast and ovarian cancers, and 3 on pancreatic cancer. A total of 10 publications were reported as clinical trials regarding cancers of the brain (4 studies), breast (2 studies), and ovarian (4 studies). Case report studies were reported in 3 publications for brain cancer, and 2 publications for breast cancer. Nearly almost of the studies found that there was a potential role of KD in the prognosis of cancer treatment. The current review suggests that cancer patients may get favorable effects from the implementation of KD to support clinical outcomes of cancer treatment.