Is additional insurance for cancer really necessary if you already have comprehensive health insurance that covers cancer treatments at "as charged"?

In the event of a cancer, indeed, health insurance can cover cancer treatment, however that is not the only concern. The additional insurance can be used to cover daily expenses in the event that the cancer stage is severe and one is unable to work, the additional insurance can also be used to cover housing loan if one is still servicing the loan as hdb will not exempt you from having to pay loan in event of cancer.
Key point is to understand what policies you already have, and determine if this additional insurance for cancer is something you're missing or simply a top up to your existing policies. A top up may seem unnecessary but it can be very useful if existing coverage are very low or insufficient if you have dependents.

Hi anon,

We need to understand how the different types of insurance work, and then you'll know why certain types of insurance are still required.

Health insurance is meant to settle your bills. You'll never see the money, the insurer usually settles the hospital bill with the hospital directly. Your follow ups throughout the subsequent years will require you to pay first and then claim back later, restoring you to a neutral position.

But then you have a problem. You don't have to pay the treatment bills, but you're still out of work and fighting tooth and nail against the beast that is cancer, going through your chemos and medications and the like. And then you realise your bank balance is depleting because, hey, you still need to eat and pay the phone and power bills.

That's where Critical Illness insurance pays you a lump sum in cold hard cash so that you won't have to stress too much about your daily expenses.

I'd say that you should get basic CI cover first for all the major CIs. Then, if you are particularly concerned about cancer, an additional cancer coverage will be helpful (but you can only claim if it's cancer)