Introduction: Older patients with cancer constitute a heterogeneous group with varying degrees of frailty; therefore, geriatric assessment with initial geriatric oncology screening is recommended. The Geriatric 8 (G8) and the modified Geriatric 8 (mG8) are promising screening tools with high accuracy and an association with survival. However, evidence is sparse regarding patient-centered outcomes. This protocol describes a study, which aims to address the predictive and prognostic value of the G8 and mG8, with quality of life (QoL) as the primary outcome. Materials and methods: In this single-center prospective cohort study, patients, age ≥70 years with solid malignancies, will be screened with the G8 and mG8 prior to receiving 1st line antineoplastic treatment. Patients will contribute medical record data including; cancer type, Charlson comorbidity index score, performance status, and treatment intent, type, and dosage, at baseline. Patients will complete QoL questionnaires (EORTC QLQ-C30 and ELD-14) at baseline, 3, 6, 9, and 12-months follow-up. Two functional measurements (the 30-s chair stand test and the handgrip strength test) will be conducted at baseline to assess the added predictive and prognostic value. At 12 months follow-up, initially administered treatment and treatment adherence will be recorded and assessed with generalized linear models, while overall survival and cancer-specific survival will be assessed using survival analysis models with time-varying covariates. The relationship between frailty (G8 ≤ 14, mG8 ≥ 6) and QoL within 12 months will be examined using mixed regression models. Discussion: Geriatric oncology screening may identify a subgroup of older patients with frailty, at risk of experiencing diminishing QoL and poor treatment adherence. With the proposed screening program, patients who require treatment modification and additional support to maintain their QoL may be identified. It is our hope, that these insights may facilitate the formation of national guidelines for the treatment of older patients with cancer. Registration: NCT04644874