Were they all x-rayed the same number of times? Same number of CT scans? Smoke the same amount and same brand? Are they the same age?
Did they die of a heart attack before the cancer in their body was discovered? (It can take 20-30 years to spot a cancer.)
Was one expiosed to fumes from work for years?
Did the one who cleans the house use a lot of toxic cleaners, such as bleach?
Finally did they all eat the same portions? Did one eat only the potatoes and skip the salad?
etc, etc, etc.