What is the age of the person we are talking about?
Is the lump present on one or both sides?
You would need to convince him/her to see a physician at least. that ways atleast the probbale diagnosis could be got.
An under lump present for 14 years is most probably benign or non cancerous; but would need a clinical examination for the list of probbale diagnosis and some investigations for a confirmed diagnosis.
Has the lump changed in size or were there any other features on breast examination like a breast lump or nipple discharge or skin changes etc?
Nothing can be advised without a visit to the physician.
Hope you are able to convince this person to see a doctor.
Do let us know about the progress.
Hope this helps.