It hasn't cured her cancer, it has gone into remission. Cancer is just a term that describes a mal-function at the cellular level, regardless of the organ involved. We are all growing "cancer" within our bodies all the time. In healthy individuals the mal-formed cells are identified as mutants and the body's defence system destroys them and reestablished a state of homeostasis at the cellular level. Cancer becomes a disease when that balance is altered and the mutant cells begin to take control. It makes perfect sense to me then, that when we suppress and modulate the body's immune response we become more vulnerable to the development of pre-existing cancers. Wouldn't the process be similar to that which happens in patients who have been exposed to tuberculosis? That is why we screen for TB prior to taking biologics. Not that it will give you TB but if you already have been exposed it may increase the chance of it becoming activated.
In this women's case she created the environment for cancer to develop by smoking. Undoubtedly she had the potential for lung cancer and her biologic medication may have tipped the balance enough to allow it to take hold. Withdrawing it restored the body's own innate defences. Unfortunately, she will probably remain vulnerable for the rest of her life of re-activating the lung cancer cells.
In the meantime, I wonder what she is doing to control her crohn's?
30+ years living with Crohn's.