A rather surprising number of chemo compounds trace directly to chemical warfare and compounds used during WWI, including several mustard-gas-related compounds.
Some years ago, a close friend died of a relatively rare and aggressive form of cancer. Among my roles was running interference against those who were pitching various miracle cures, with that tired old scam laetril playing a significant role.
In the decades since, I've watched developments in the science and development, as well as traced the history. It turns out that the treatment received a few decades ago was little changed from that of the 1960s, and has progressed little since. Genetic sequencing identified the affected chromosome of the triggering mutation in the 1980s, and we now know the specific codons involved. There remains no cure.
Five year survival remains about 20%. Laetril is still a fraud. And several of the other patients we came to know during the course of my friend's treatment have died since of conditions related to the treatment itself, though yes, they did buy another 10--20 years.
Cancer is brutal.
I will note: "cancer" is a symptom cluster manifested by malignant growth, and virtually always due to genetic mutation within the affected cells (I'd say "always" though I'm not completely sure of that). The specific triggers, and the possibilities for cure, vary tremendously. Some bladder cancers are virtually entirely treatable by, of all things, tuberculosis baccili. Skin cancers if caught early pose little risk. Others are tremendously aggressive, and an online friend's posts progressed from announcing their partner's diagnosis with liver cancer to the partner's death over the course of less than two months.
Broad-brush statements are virtually always false.