Sorry to hear Alex.
We are at a similar stage with our 12.5 year old yellow Lab. She is a great girl but has osteosarcoma on her front right leg and spreading slowly to her lungs. The meds have helped for a few weeks but she is starting to limp a bit more even with the meds. I just hope she lets me know when the time is right.
Here is a picture of her (Citrine) with her best buddy (Yara).