Despite significant progress in cancer diagnosis, treatment, and overall disease management, cancer remains a major global health challenge. Immunotherapy has transformed the therapeutic landscape by harnessing the immune system’s ability to recognize and eliminate malignant cells. In particular, immune checkpoint inhibitors have demonstrated substantial clinical success. However, their systemic administration is often accompanied by high rates of immune-related adverse events. Intratumoral delivery has therefore emerged as a compelling alternative, offering the potential to modulate the tumour immune micro environment locally while minimizing systemic toxicity. Yet, its effectiveness depends critically on achieving precise injections and ensuring adequate intratumoral distribution of the therapeutic agent. To address this need, we present a novel extension of an already validated a multiphase porous-medium model, now enhanced to characterize drug transport and tumour response following intratumoral immunotherapy administration. In this multiphase porous-medium representation of the tumour micro environment, the extracellular matrix acts as a solid scaffold, while tumour cells, immune cells, and interstitial fluid occupy the pore space. Building on the original model, this work introduces the therapeutic component by explicitly incorporating the therapeutic agent, αPD-L1, as an active species, together with oxygen as the nutrient governing tumour growth and necrotic cells generated under nutrient deprivation. Each constituent’s volume fraction evolves according to partial differential equations combining two classes of phenomena: mobility terms describing advective–diffusive fluxes within a poroelastic matrix, and reaction terms representing local biological mechanisms such as proliferation, death, metabolism, and immunotherapeutic response. By analysing how different immunotherapy delivery strategies influence drug distribution and tumour evolution, this work aims to identify conditions that optimize therapeutic efficacy and reduce reliance on repeated injections. Ultimately, this represents a first step toward a prognostic tool that could support physicians in personalizing treatment, adjusting dosage and timing, and minimizing potential side effects.