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Q. Is the lump round?
Q. Can you pinch the skin over the lump, is it attached to the skin?
Q. Is the skin over the lump red and swollen?
Q. Is the lump moving under the skin?
Q. Evening fever, night sweats, loss of appetite?
Thanks for the details.
A lump in the area of lymph nodes is always taken to be a lymph node unless proven otherwise. With the clinical features you have mentioned, it has all the characteristics of a lymph node. Axillary lymphadenopathy can be a result of many acute or chronic infections and might be idiopathic (without a cause) in some cases.
However, the next step would be to get it physically examined by a Primary and get a Fine Needle Aspiration Cytology (FNAC) done. This will tell us the nature of the lymph node and point towards a more definitive diagnosis. The test is done in a laboratory or the clinician's office as a local procedure with a fine gauge needle. Results are available after 3 days depending upon the laboratory's protocols. It is a very sensitive test for lymph nodes and gives the diagnosis is almost all the cases.
If it is not causing you discomfort and is without any significant symptoms then you can wait. If it goes away in a week that means that the hypertrophy/enlargement was physiological and due to defense against a certain infection that has been dealt with by the body's defense mechanisms. Yes, you can wait for a week if it is okay with you.