So, why don't cancer treatments work here? Or would they likely work here but they largely haven't been tried yet? (See also codetweep's comment about surgery.)
Endometriosisis is 'benign' in the self-contained sense only. I would imagine that changes the target profile. I don't think there is are any rigid 'out of scope' policing drugs or biological mechanisms for that. As opposed to cancerous malformed biomarkers which scream "I shouldn't exist!" to the immune system.
I doubt chemotherapy drugs have a favorable risk/benefit ratio. The original article notes that somatic DNA changes might be involved, so perhaps immunotherapy might be useful. Interestingly this is being studied [1].
