American Red Cross's exclusion guidelines dictate lifetime exclusion for blood donors whose cancer has had "recurrence", including non-blood cancers, which have never been known to be transmissible via blood products. (Their specific wording is that donation is acceptable if it was a non-blood based type of cancer and "the cancer has been treated successfully and it has been more than 12 months since treatment was completed and there has been no cancer recurrence in this time.) As Mayo Clinic is doubtless aware, survivors of prostate cancer after prostate removal and other primary therapy sometimes land in an ambiguous situation, where non-zero PSA recurs subsequent to primary therapy, but then hormone ablation therapy (leuprolide acetate or similar) reduces PSA back to below the measurement threshold, and it remains there for many years, perhaps a lifetime.

The ambiguity lies here: There is no evidence of remaining disease, but patient may and probably does have latent cancer cells in one or more distal locations (since, the post-excision measurable PSA could only have been emitted by escaped cancerous prostate cells), but, as long as leuprolide acetate therapy then keeps PSA below measurement threshold, and no tumors show up on medical imaging or via palpation, patient's cancer cell colonies' continued existence can only be suspected, not confirmed. If patient is really lucky, normal cell apoptosis and T-cell activity might even have invisibly ended the cancer, but that happy outcome cannot be confirmed, either: All cancer evidence for such a patient / cancer survivor remains indirect, as long as the latency lasts.

Such a donor, answering the screening questionnaire, ticks "yes" on the "Have you had cancer?" question, then the screener asks if it's been one year since completion of treatment. And, well, the correct answer depends on what one means by treatment:

Donor is getting periodic leuprolide acetate "depot" injections to suppress androgens, and is continuing to see PSA < 0.1 ng/ml (unmeasurable) blood-test results, say, for one-year plus. Yet, whether he has had "recurrence" of his non-blood-transmissible-as-far-as-science knows cancer is a judgement call, isn't it? (It depends on how you construe "recurrence".) Is American Red Cross going to enroll the donor onto a lifetime deferral list, merely for walking into one of its clinics and accurately answering screening questions? Would Mayo Clinic Blood Donor Program do so, if he goes there?

Also: Is hormone ablation deemed prostate cancer treatment for purposes of the "completion of treatment" screening question?

Also: Is patient's donation ethical? All medical literature on the subject seems to say solid-organ cancers have never been transmitted via blood products, but much of that literature perversely suggests donation following "cancer recurrence" should be avoided anyway, as cancer cells might be present despite this never having been known to occur, and could cause cancer in an immunocompromised recipient. So, do we know enough to exclude that possibility with high confidence, or don't we?