Hi, try with the literature:

Article MicroRNA Isolation from Formalin-Fixed, Paraffin-Embedded Tissues

This researcher they are on researchgate so eventually you can ask for help

or this

Article miRNA expression profiling of formalin-fixed paraffin-embedd...

You can also download the datasheet of the kit used to understand better the procedure

or this

https://jmd.amjpathol.org/article/S1525-1578(10)60151-1/fulltext

All this protocol are validated and you can email the authors just in case

Sorry but I answer here the question about DNAse, it is only for convenience.

If you use a kit where it is point out that you can use DNAse you can do this but if the datasheet kit don't specify this part i don't recommed you. When you using the kit for extraction or miRS enrichment, in particular with low concentration of miRs in the samples, the column procedure it is emough to have clean miRs, the difficult is the yield.

I think that you have low yield and the DNAse passage, after using hte column, it is not a good thing. In my case miRs from serum (low yield) my datasheet kit (Qiagen) don't recommend the use of DNAse

Thanks a lot Valeria