Dr Gaya qualified at St George's Hospital Medical School (University of London) in 1995, where he was awarded a distinction and several academic prizes. He trained in Clinical Oncology at Imperial College and St Bartholomew's Hospital, and subsequently undertook a Cancer Research UK MD Fellowship at University College London. He has been a Consultant Clinical Oncologist at Guy’s and St Thomas’ Hospitals since 2005. Dr Gaya specialises in the multimodality non-surgical treatment of skin cancers and gastrointestinal tumours using chemotherapy, radiotherapy, immunotherapy and biological therapies. This includes colon, rectum and anal cancer, and cancers of the oesophagus, stomach, biliary system, pancreas, and liver.

Dr Gaya's main research interests are in the areas of functional cancer imaging, and immunotherapy of cancer. He is researching ways to assess response to treatment much earlier, and also boosting the immune system to fight cancer. He is heavily involved with the implementation of the latest radiotherapy techniques such as IMRT, IGRT and Tomotherapy, and stereotactic body radiosurgery. He was one of the first UK doctors to use the CyberKnife unit. He has published widely in peer-reviewed journals. Dr Gaya also offers a personalised medicine service which includes full cancer gene sequencing and chemotherapy sensitivity testing using mouse PDX models. This can often lead to implementation of novel therapies with considerable success.