No matter how small a lump, it may still be malignant and very dangerous. Sometimes we are more or less concerned depending on what a fine needle aspirate reveals about the lump.
Minor Lump Removal is certainly indicated if there is a suspicion of malignancy, and in fact the earlier and smaller it is when detected the better. Some small lumps may not be considered dangerous but may be removed because of their location. Examples of these include eyelid lumps that may abrade and irritate the eye. Rectal lumps are also worth taking off, because of where they are and the complications of trying to remove them if they grow larger.
If a lump is small but considered dangerous, we will still take a very wide margin of tissue around it in order to minimise the chance of re-growth. If it is considered to not be such a concern then we may leave it all together and just monitor it, or remove it with just a small margin, especially if in a complicated area such as the eyelid.
The only way to definitively identify the tumour is to send it to pathology. A pathologist can determine exactly what the lump is, and rate the likelihood of its spread or return. With this advice we now have options as to whether further surgery is warranted, or even radiation or chemotherapy.
All lumps should be checked by your veterinarian. If of reasonable concern then biopsy or surgical removal may be warranted. Upon surgical removal, pathology is the only way of determining the exact nature of the tumour. If pathology reveals a significant degree of malignancy, further options are available to reduce the chance of spread or recurrence.