Natural selection: polar bears.

[Rhino1000]

If a polar bear has a gene allele that causes cancer in old polar bears (after their reproductive years have passed), does that allele affect the bear's fitness?

According to the book, it doesn't (which I would agree with), because it doesn't affect the bear's ability to pass on its genetic information. However, this seems likely to affect the survival of any bear cubs that might still be in the maturing process. Does this mean that the allele would reduce the fitness of the bear cub? Thoughts are welcome.

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[DrknoSDN]

The scenario is basically changing the environment. You could also say both parents die during labor. How does this change the offspring fitness?
If you change the environment you can change how "fit" an animal is so yes, killing the parents can make the offspring less fit.

Quite similar to kin selection scenarios. Having guardians survive long past reproductive ages to ensure children and grandchildren reproduce will increase the fitness of the offspring and select for the gene allowing longer survival.