@kalleem1, It must be deflating to hear that her breast cancer is back and has spread to her lung. This is rightfully a scary time but knowing that the breast cancer is driving the cancer growth can help determine the best way to treat the disease. There are different drivers between the two types of cancer. Breast cancer has many advanced treatments available now that weren't available even five years ago. There is real hope in the breast cancer realm.
The decision to wait for biomarker tests versus starting chemo now is highly dependent on her overall health right now and how long the tests results may take to come back from the lab. You may want to ask her doctors what the risks are of waiting, and then you and she can weigh those risks. Some people need to take action right away so they feel that they are doing something, anything, to fight the cancer. We often have time to research and make decisions (as long as she is stable and her overall health isn't at risk, or she is not suffering too much).
The Breast Cancer group may have suggestions on treatments specific to breast cancers too. Here's a link to that group. https://connect.mayoclinic.org/group/breast-cancer/

Hi @kalleem1, as you likely know, breast cancer that has spread to the lungs is called metastatic breast cancer. Because your wife's cancer cells are breast cancer that has spread to the lungs, her treatment may not be the same as treatment for patients who have primary lung cancer. I hope that makes sense.

For that reason, I encourage you to follow the discussions in the Breast Cancer support group here: https://connect.mayoclinic.org/group/breast-cancer/