Hello, I have understood your concern over the blood test results.At first, it would be even better if you have provided us with the actual count of the B12, RBCs, WBCs and any other test results if you have done and also for how long he is having this condition.But as per your description, I might be able to help and clear few doubts. Your husband is taking treatment for prostate cancer which included 49 radiation treatments and hormonal therapy.You mentioned the last PSA levels .39 which I am not clear about its unit but, comparing it with normal levels which are 4.0ng/mL or low.It appears that the levels are in normal range.Next thing there are effects of radiation therapy on your body and blood like the smaller size of the WBCs, it usually occurs due to the radiation treatment and generally seen in other conditions like autoimmune diseases, due to some medicines like antibiotics or bone marrow damage.Here the cause can most likely to be the radiation therapy. About the B12 levels that are low, it also has many reasons, few of which can be these. Any history of surgery related to removal of stomach or part of it in past? As this is also commonly seen in bacterial overgrowth which decreases absorption of B12 or it can be a dietary deficiency if he is a vegetarian then there high chances that this could be the main reason.As a result of low level of B12, there is an increase in the size of the RBCs or abnormal large size of RBCs is seen. I would suggest you, to do follow-up and take the advice of the doctor who is treating your husband so that further management will be done to correct the levels.Or necessary steps could be taken.I hope this helps.If any queries or doubts do feel free to contact.Stay healthy and fit.