What is the percentage of her2 breast cancer recurring if I stop taking femara (letrozole) which I have been on for 2 1?

Talk to your onc. Your oncologist would be the best one to answer this question. It's not a good idea to stop taking med without a discussion with the prescribing physician, especially when cancer is involved.
Do not stop. Letrozole (femara) is a non steroidal armatase inhibitor decreases estrogen production do not stop with out talking to your oncologist, any cancer in remission may recur if medications are stopped with out your doctors advise.
Higher than if u... ...Stay on femara (letrozole). To be more direct, your question cannot be answered since we don't have info re: your stage, rx to-date, personal health, etc. Regardless, people sometimes minimize the effectiveness of aromatase inhibitors--they are potent chemotherapeutic agents, proven to help cure breast cancer. The current recommendations (5 years) are based on sound clinical trials. Please don't stop.