yet another question?

Both parts of your question depend on the genetics of the tumor cells. Here's the eye-glazing biology lesson. In the middle of every cell is the nucleus containing the DNA blueprint of the cell. When the cell divides, the chromosones do too, making each daughter cell an exact copy of the parent cell. Sometimes when the cells divide, the chromosones don't match up just right and the baby cells are messed up copies of the parent cell. Usually the body cues in on signals sent out by the cells themselves that they are messed up and the immune systems destroys the messed up cells. In the case of cancer cells of course they missed the first set of messed up baby cells. Baby cells grow up and divide. Messed up cancer cells grow up and divide too. But because the nucleus of the cells is messed up, the resulting baby cells are LIKELY to become even more messed up as the process of growth continues. [Beleive it or not, these messed up cells look messed up under a microscope. The cell shapes are not as regular as the tissue from which they sprang and the middle dark nuclei are really weird looking. A pathologist can see how aggressive the cancer is by seeing how many cells are in the process of dividing in a given sample of cells. He can also tell how different they look from normal.] Also, one of the things that is possible to happen as these messed up cells develop, is that they progress to something that can break off, travel around, and set up camp elsewhere. You know you cannot see a cell without a microscope. It takes a cell awhile to grow and divide. Some breast tumor cells divide every 27 days (very fast growing, aggressive cancers), some divide only once every 220 days (very slow growing, non aggressive cancers). I read about a cancer in the throat common in Africa where the cells double every 7 days. It takes lots of divisions before the cells are big enough to make a lump, so any cancer found by mammogram, MRI, PET/CAT scan, ultrasound, or feel has been there for anywhere from 2.5 years to 8 years before we find it. Here's the answer to the second part of your question. Some nuclei in the messed up cells are messed up in such a way from the very first division that they can travel and set up camp elsewhere (that is, they can form metastases in your lymph nodes and throughout your body). Some develop it after messing up divisions later. Some never develop this ability. Doctors sample the lymph nodes to see if cancer is there. If it is, it signals them to use a more aggressive treatment (chemo) because they are dealing with a more aggressive cancer. Cancer cells can also travel through the blood stream, but since they usually travel FIRST through the lymph system, sampling that has been a good enough judge of when to use chemo for an aggressive cancer. Blood tests or possibly even swab tests of your spit are on the horizon. When they are perfected we will be able to skip the mammogram and node operation and just go to the doctor or the dentist for a swab of our spit. I look forward to that day for my nieces and granddaughters. In the meantime, I guess we are stuck with node sampling to judge cancer aggressiveness.

We often hear of how the cancer is encased in the tumor where the cells are multiplying within the actual tumor not being released into the body.
At surgery there is risk of cancer cells seeding themselves in the area of surgery I also was told often the reason for actual radiation if my memory serves me correctly which often does not...
Tumors left too long have a higher risk of infecting the lymph nodes. I am survivor of Stage 3 invasive carsinoma breast cancer with 11 out of 21 nodes positive at the time of diagnosis. Yes the treatment was very aggessive and I did have two mastectomies at different times and took everything they had. My grandmother didn't fair as long of a survival and the treatments more aggressive back then.
I was 36 at the time of my diagnosis and am grateful for everyday I have had.
I found I had to be my own best friend along the way instead of giving it all away.
Tara