Cancer immunotherapy has transformed the global oncology landscape, offering durable responses across malignancies once considered untreatable. In Asia and Southeast Asia, regions facing a rising cancer burden, countries such as Malaysia are progressively integrating immunotherapeutic approaches, including immune checkpoint inhibitors and CAR-T cell therapies. Regional progress is supported by investments in research infrastructure, expanding clinical trial participation, and cross-border regulatory collaboration. However, significant challenges persist. Diverse genetic and epidemiological profiles complicate treatment generalizability, while disparities in healthcare access, limited biomarker validation, and high costs restrict widespread implementation, particularly in low- and middle-income settings. In Southeast Asia, including Malaysia, these challenges are intensified by urban-rural disparities in healthcare access and financial limitations. However, emerging opportunities such as biomarker-informed precision immunotherapy, artificial intelligence-enabled treatment personalization, expanded telemedicine services, and enhanced access frameworks offer promising pathways forward. This review highlights the current landscape, ongoing challenges, and future prospects of cancer immunotherapy in Asia and Southeast Asia, with a particular focus on Malaysia’s growing role in this evolving field. Cross-regional cooperation, regulatory harmonization, and personalized treatment strategies are crucial for equitable access to cancer therapies across this region. By synthesizing fragmented and underrepresented evidence from Southeast Asia within a broader Asia-focused immunotherapy framework, this review aims to provide a consolidated reference that can guide future research prioritization, strengthen regional policy development, and support the design of more inclusive and scalable immunotherapy implementation strategies.