How often should a 40 years old women to be checked by physicians for fear breast cancer?

Debated.: Depends. Every other year is probably OK unless you have mother / father / sister or brother with breast cancer. Mammogram is reasonable every two years although I believe Europe is now advocating less. I am unaware of your countries screening guidelines

Yearly: Unless other risk factors, yearly clinical breast exam and mammogram every 1-2 years until 50, then yearly.