Tumour markers can be unreliable, that is true. But a polish lab nurse did a CA15-3 test on me ( here in Ireland you don’t usually get them as they are deemed unreliable) and it was 285 last April ( under 30 is normal). By June it was 365. So I’d say in my case it was prudent to take it further. I had no other symptoms. As you had a double mastectomy you probably didn’t get Radiotherapy which is good. One of the common causes for bone cancer that was mentioned is previous radiotherapy for instance. ( which i had in 1999). I didn’t consider myself as ‘cured’ either as I am aware that cancer reoccurrence is likely when you have had it before. But when 23 years go by and you feel in the best of health - I’m 72 and still work 2 jobs - you do stop thinking of it daily. For me it was like knowing that I’ll die someday, as we all do, being aware it could be today or tomorrow even but in my everyday life the survival instinct makes you experience it more on the rational level. Just saying, better be safe and ask for regular check ups.