A number of statistically predictable causes and correlates of cancer are, of course,
known (E.g., smoking).
But is there any estimate of the percentage of cases that are statistically unpredictable results of mutation?
Well, breast cancer is a major killer, and that is the result of a specific gene that can be identified by genetic analysis. Christina Applegate underwent a lumpectomy, but after learning that she had the BRCA genetic mutation (aka, the breast cancer gene), she opted for a double mastectomy. Of course, that isn’t “unpredictable”. It is, in fact, quite the opposite. Genetic mutation resulting from damaging solar radiation is rather unpredictable. Some “sun worshippers” spend an entire life on the beach and never develop cancer. Others develop it just from the exposure they get playing golf in the sun.
Not really. That’s why sun exposure is a known risk for skin cancer.
AIUI, all cancers are due to genetic mutations. I think your question has to do do with what percentage of carcinogenic genetic mutations are due to identifiable external factors (e.g. inherited genetic defects, smoking, exposure to ionizing radiation), and what percentage are “spontaneous.” The latter is in quotes because, ISTM, these aren’t necessarily cases that absolutely weren’t caused by external factors - it’s just that any external factors that may have played a role couldn’t clearly be identified. Example, you are diagnosed with lung cancer, but you have no family history of the disease, you never smoked, and you can’t point to any exposures to known carcinogens - it’s just that you had absolutely no idea that you spent your entire childhood in a house with dangerously high radon concentrations. Or that you got hit with a particularly high-energy cosmic ray in your 30s. Or that you have an unusual defect in your DNA replication/repair machinery, and that you were simply destined to develop a fatal genetic error at some point in your life, and it just happened to be in your lungs.
At one level, all cancer is a result of random mutation. Every other “cause” of cancer operates primarily by increasing the chance of mutation in one way or another. Carcinogens in tobacco smoke damage DNA. The BRCA gene codes for a protein involved in DNA repair, so people with pathogenic BRCA variants don’t repair damage as well, leading to mutation. And so forth.
Ultimately, it’s all but impossible to track down THE specific cause of any one specific cancer. The best you can do for what you’re asking is narrow your numbers down by dropping out familial cases (cancers in families where genetic causes are implicated) and other known risk factors (smoking, etc). But it’s still going to be a pretty rough estimate.