That sounds so stressful!! I hope his pain is well-managed!!
Yes, melanoma can metastasize to bones. It could also be a soft-tissue mass pressing up against the spine, but not necessarily in the spine itself (that's what happened to my husband).
My husband also experienced increasing back pain and got an MRI to see what was going on. The PET scan showed active disease, but my understanding is that the doctors wanted a clearer picture with the MRI so they could decide what to do. There was a chance that some surgical procedures would be possible to reduce my husband's back pain (it was excrutiating and also paralyzing one of his legs). Ultimately the MRI resulted in my husband receiving a steroid epidural, which fixed his pain pretty dramatically.
Don't lose hope yet. There is also a chance that there is some other damage, not cancer-related, in your husband's spine. For a long time my husband's doctors did not think his back pain was cancer, since his treatment was working so well elsewhere! They believed that other problems were much more likely (of course, they ended up being wrong, but it goes to show you that there are a LOT of non-cancer back pain issues out there so we shouldn't leap to a cancer diagnosis without more investigation). The MRI will allow the doctors to come up with a good plan of attack, whatever the problem ends up being.
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