This is early research but interesting. If it is true, I doubt it is a major cause as then we would see a geographic distribution of brain tumors that mimics the distribution of Lyme disease cases which we do not see. However, if there is a link, that may be the reason Doxycycline might help brain tumors. Doxycycline is an old oral antibiotic - very safe - that is used in the treatment of Lyme disease which is caused by a bacteria. It is also part of the Care Oncology Glioblastoma Protocol, which is a cocktail of repurposed drugs used to treat Glioblastoma - and which has reported some success!