Whales do get cancer, the paradox is why they don't die of cancer at higher rates than humans given their larger size. The answer is metabolic in nature, larger animals have much lower basal metabolic rates and genes regulating cellular metabolism are key oncogenes. There is much discussion about transcription factor p53, which is known as a key tumor supressor, but it's important role in regulating metabolism was overlooked until recently. https://www.ncbi.nlm.nih.gov/pubmed/30500901 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5955117/
I thought it likely its because they don't go to the quacks for diagnoses . After all if a doctor doesn't recognise it it doesn't exist .