Thank you for the additional information.
Many pet owners give this medication to their cats. I have had many clients give it with no problems to their own health. Also, I have not heard of any person having a problem from giving this medication to their cat. But, anything is possible. In general, I tell my clients to take precautions. It is more a situation of better safe than sorry. It is better to handle the drug carefully and educate owners so they have a healthy respect for the medicine.
Since I am not a human doctor, I can't comment on your husband's previous medical history and handling chlorambucil. You could always check with your family physician. One extra precaution to take is for him to not administer the medication.
The reason that clients are cautioned when handling chlorambucil is because it is an alkylating agent. This is a type of chemotherapy drug that can be carcinogenic (cancer causing) and teratogenic (damaging to a fetus).
I recommend that owners handle the medication with gloves and wash hands immediately afterward. Children; women who are pregnant, trying to become pregnant, or nursing, and immunocompromised people should not handle the medication at all.
Tablets should NOT be split or crushed. For the most part, the drug is broken down into inactive ingredients before it is eliminated from the body in feces, but trace amounts of intact drug might be present in feces, urine, and possibly saliva (especially right after oral administration).
I do not routinely recommend limiting contact with the cat (kind of defeats the goal of quality of life), but I do recommend that gloves be worn when scooping or cleaning the litter box.
And anyone who shouldn't be touching the drug shouldn't be handling the litter.
The risk to the you is minimal, but with these simple precautions, the risk can be almost zero.
So, for your situation you may want to discuss with your vet the possibility of changing the dosing schedule so you do not need to split the tablets. The tablets have a coating on them. When you split them, there is more likely of exposure to the medication.
Another option would be to consider injectable chemotherapy administered at your vet. Not all vets that are not oncologists are comfortable with the dosing or administration, but you could ask.
Here is an article about chlorambucil:
Please let me know if you have any other questions or concerns. I am here to help.