Thyroid cancer and smoldering myeloma is there a link?

No: Both are common. I know of no genetic syndrome that increases the likelihood of both. I hope that your thyroid cancer was found early and has been cured, and that the myeloma remains quiet as it often does.

Thyroid and myeloma: I don't know of any relationship between thyroid cancer and myeloma, but people with autoimmune thyroid disease have an increased risk of multiple myeloma. Hope this helps.

Cancers: There is no link which i can think of. People with one kind of cancers are prone to get other kinds of cancers.