Gangadharan started his career as a tutor in the Department of Radiotherapy and Medical Oncology, Thrissur Medical College. He then joined RCC, Thiruvananthapuram in 1989 as Assistant Professor and Head of Department of Medical Oncology. He participated in the Bone Marrow Transplantation Training Program in the US in 1995 and in the UK in 1997 with the Fellowship assistance of National Cancer Institute and the World Health Organization. Gangadharan has published more than forty articles in national and international journals and also conducts cancer awareness through various media, awareness classes and camps. His lessons were included in three Medical textbooks. Received more than 60 awards at the state, national and international levels for his outstanding contributions in the field of cancer treatment.