Yvette, I'm sorry to hear that your mother's breast cancer has spread.  One important point to clear up is whether she has breast cancer that has spread to her lungs or whether she has lung cancer--a new cancer that started in her lung, not in her breast.  If she has lung cancer, there are different drugs used to treat it than if she has breast cancer that has spread to her lungs.

It's impossible to predict what will happen.  These days some people live a long time with breast cancer that has spread to the other organs.  I heard just the other day from a woman who was first diagnosed with breast cancer nine years ago, with a spread of the breast cancer to her bones six years ago, and another spread of the breast cancer to her lungs three years ago.  She lives an active life, playing golf and getting regular treatments to keep the cancer under control.

However, a spread of breast cancer to her lungs is a serious development, and you are justified in being very concerned.  I hope the next drug the doctors try stops the spread of the cancer.  She might want to see if there are any clinical trials of new drugs for her to try.