You are correct. Some studies have shown that prolonged antibiotics cause increase risk of cancer. There was roughly a 2-fold increased risk of developing breast cancer compared to the control group.
Velicer, C.M., et al. Antibiotic use in relation to the risk of breast cancer. Journal of the American Medical Association. Vol 291 (February 18) Pgs 827-835. 2004.
I always use caution when reading these types of studies because I believe many of them over-emphasize the associated risks (but that is my personal opinion). Drinking, being obese, working night-shifts, short-term antibiotic usages and about a billion other things cause an increase risk of cancer.
Obviously, none of us want to be on long-term antibiotics. There are some potential consequences with doing so.....but I think I'll take my chances.