I had previously had a blood clot 10 years ago when I broke my leg in three places and was laid up. My calf muscle started aching a little bit and then got a little worse. When I pulled my toes towards me, I could feel it and knew from my previous experience it was a clot. Blood clots are a possible side effect because the chemo makes the blood sticky, and the veins become compromised. I do a lot of research on reputable "teaching hospital" web sites about everything related to my very rare breast cancer and this was something I found on the MD Anderson Cancer Center site. I have to limit my walking for a week until the clot is dissolved, but am concerned that I have only had two treatments out of the many for the next 6 months and was told at my "second opinion visit" at the Mayo Clinic, Rochester, 'Don't sit around after each chemo therapy treatment, get up and walk every day no matter what and drink lots of water". I hope this helps! Chris