As the medical community continues to explore and harness the potential of biosimilars, it is imperative to accumulate robust real-world evidence (RWE) to guide informed decision-making, and enhance patient outcomes in cancer treatment. This article reviews the current understanding and utilisation of biosimilars in the treatment of breast and lung cancers by reviewing existing RWE. A literature search of PubMed, MEDLINE, and Scopus was performed to analyse observational studies pertaining to the adoption of biosimilars in people living with breast or lung cancer, with publications considered since 2019. The review summarises the current RWE relating to biosimilar use for its approved indications across breast and lung cancer. Despite the scarcity of evidence addressing the cost-effectiveness of biosimilars in breast and lung cancer treatment, biosimilars may offer a dual benefit by enhancing patient outcomes, while ensuring cost-effectiveness, thereby increasing access to oncology therapies globally. The increased access to biosimilars within community oncology practices, hospitals, and national healthcare systems, promises substantial cost savings. This review highlights the evolving landscape of biosimilar utilisation in oncology, revealing their potential as a more affordable and inclusive approach to cancer care, while also indicating areas for further research.