There are a lot of papers out there. I haven't seen any name a specific carcinogen but it seems like the papers average around a 2x increased risk of firefighters developing brain cancer. This review is a good place to start (https://www.ncbi.nlm.nih.gov/pubmed/23022824) as it references a lot of other studies. However, most of the papers I've seen mention 'gliomas' or 'astrocytomas' broadly speaking, or even just 'brain cancer'. So it may be difficult to find data on what the risk is for firefighters of developing a specific histologic grade of glioma, such as anaplastic astrocytoma.