People with PCOS (such as myself) might be at an increased risk of cancer because of various physiological (e.g. hormonal) imbalances. One of the ways in which these imbalances manifests is through erratic periods. However, if a woman without PCOS does not get her periods, she is not necessarily at a higher risk of cancer. So she might be ok with using an IUD that stops her period (there's research backing this up), whereas this might not be true for some people with PCOS.

The important thing for a woman, regardless of whether she has PCOS, is to consult contraceptive decisions with a good doctor. Each woman's body and health risks are unique.