Brief Answer:
May be a lipoma or a sebaceous cyst as the commonest cause

Detailed Answer:
Hi.
Thanks for your query, albeit small.
Noted the history of a soft lump next to the spine, X-ray confirms this to be not a scoliosis.

First of all, a soft lump can not be scoliosis as scoliosis is of the spinal column bones.

The commonest causes are:
- Lipoma
- Sebaceous cyst.
- Abscess or collection of any fluid.
- Also noted history of breast cancer (details not given), a secondary of breast cancer may present the same say (although very rare in such a form).

Most of the things can be diagnosed by clinical examination and MRI helps to confirm the diagnosis.

Please let me know a few details:
- Since when have you got this lump?
- Size, shape, mobility ?
- Any black spot as if with which is is attached to the skin (suggestive of a sebaceous cyst).
- Moving freely under the skin and above the normal muscles - suggestive of a lipoma.

Get a clinical examination done by a General Surgeon, FNAC if required and best way is to get a confirmatory MRI if your General Surgeon says so.
Excision of such a lump helps in two ways:
Once your get the disease out of hte body, which is not the normal part of the body.
Secondly, you get a confirmatory diagnosis by histopathology of the excised specimen.

I hope this answer helps you to get a proper diagnosis, and get a proper further treatment. Please feel free to ask for more or if you need further clarifications or if you feel there is a gap of communication.

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