In addition to the previous answers, one of the terms that you may hear when healthcare providers are talking about cancer is 'mets.' For instance, "lung cancer with mets to the brain." This is short for metastasis and just means that, as the other answers have explained, that the cancer has spread to other organs or sites. The plural of metastasis is metastases so since both singular and plural are a bit of a tongue twister, you may hear mets.
For those of you who like to know where words came from, metastasis is derived from the Greek word meaning displacement meaning "shift" or "movement."