Thank you for asking your query at DoctorSpring.
A soft swelling , which is superficial, which is present for years, with not much changes (I assume) is most probably a Lipoma or a benign cyst over a tendon. The swelling very well fits into the description of a Benign (non cancerous) swelling. So unless you want it to be removed for cosmetic reasons, you can just ignore it.
The only definite way to know the exact composition of the swelling is by doing a needle biopsy. (FNAC)
Hope this helps
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