Making cancer visible – Dyes in surgical oncology

• Dyes have roles in the aetiology, diagnosis, and treatment of cancer.
• Synthetic dyes particularly coal tar dyes can be carcinogenic.
• Dyes are used to identify cancer, and are especially useful in intra-operative imaging.
• Dyes inspired the birth of modern chemotherapy, and can be used as chemo-ablative agents.
• Theranostics is a new field where the same agent (such as a dye) can be used for both diagnosis and therapy.

Dyes share an intricate relationship with oncology. Dyes can cause cancer as chemical carcinogens, but can also be harnessed against cancer when used as diagnostic and therapeutic agents. Histopathology, imaging, and newer molecular diagnostics all rely on dyes, and their use in sentinel lymph node biopsies and intra-operative imaging has helped drive a paradigm shift in cancer surgery towards minimally-invasive and organ sparing approaches with enhanced resection accuracy. As therapeutic agents, the cytotoxicity of specific dyes can be employed in direct chemo-ablation or in photodynamic therapy. The same agent can have dual functionalities in cancer detection and treatment, in a novel field known as theranostics. This is facilitated by newer generation dyes conjugated with tumour-targeting probes such as antibodies, and these bio-conjugate agents can also incorporate nanotechnology or radio-isotopes. Further advances will be closely aligned with our increasing understanding of molecular oncology, and will form a new generation of cancer detection and treatment agents that promote precision medicine for cancer. Dyes and their roles have evolved and been reinvented, but they remain relevant as ever. This review explores the fascinating history of dyes, and their place in the state-of-the-art of oncology.