Would a cancerous (lymphoma, breast cancer, etc.) axillary lymph node shrink?

No. A lymph node replaced with malignant cells growing as a primary lymphod tumor or metastatic from another site which has spread to axilla will not shrink without treatment, either chemo or RT. The node will enlarge further or if unchanged will spread to adjacent nodes. It does not have the potential to metastasize further to non lymphatic tissue such as liver or lung.
Only if body immune. system were to respond to a cancer versus continue to let it grow (as is necessary to get to a size detectable by any current means beyond accidental discovery under a microscopic or by one of the current tests which can partially detect a few cancers before very advanced, e.g. PSA. In practice) because this is huge change in behavior, extremely rare. Thus if node shrank, likely not a cancer.

Related Questions

22yrs old mammogram normal enlarged right axillary lymph node 7mm left axillary lymph node 3mm waiting biopsy results. Family history breast cancer?

Be patient. Even with a family history of breast cancer, it would be very rare for a 22 yo to have the disease. You only have about a 14-15% chance of developing breast cancer, unless there are multiple family members who have the disease. There are many reasons for lymph nodes to enlarge, many benign, so just wait for the results. Good luck. Read more...
Lymph node biopsy? The most common reason lymph nodes enlarge is simple inflammation. In this way they help ur body fight infections. If ur mammogram is normal and u have no suspicious breast masses on exam your risk of cancer is very low. The family history increases that a bit. But it depends --were the relatives who got breast cancer old or young when they got it? If young, risk is higher. Md should counsel. Read more...
Further eval needed. What kind of family history? You may be a candidate for brca testing. Check out www.Myriad.Com for more info about whether you meet criteria for testing, or contact me with more information so you can be better advised. Read more...

What are the characteristics of a cancerous armpit lymph node from breast cancer? Hard, immobile, etc?

Not easy to tell. It's common to have a palpable node or two there. Metastatic disease tends to produce large nodes and they may be matted and/or fixed to the chest. If you have no breast mass and the nodes aren't obviously abnormal, I wouldn't worry. Read more...