MRI scan

I had a masectemy on my left breast, grade 3, just finished my 4th course of TAC chemo. A week after diagnosis had an MRI scan to show that didnt spread but something showed up on my right breast, had another ultrasound where 3 cysts were drained and all ok but still have to have another MRI, very concerned but my consultant advised me that at this stage of of my chemo (only 2 to go) this is normal and he thinks it is just breast tissue (what is breast tissue???), and nothing to worry about!!! Why do they say that (and my consultant is quite direct!!). Would the chemo have killed off anything that may have been lurking in my right breast, 2 oncologists have checked me and cant feel anything. Just wondering if anyone else has experienced this, not too many depressing stories please as cant cope with any more bad news.