Lumps in and under the skin become more common with age and can have many different causes. Fatty lumps are common, but tumours that need treatment can also feel soft and movable. It is therefore safer to identify a new or changed lump than to try to judge it with your fingers alone.
The vet measures and feels the lump and can often take a cell sample with a fine needle. Such a sample can give important information without a larger procedure, although some changes need a tissue sample for a reliable diagnosis. If you find a lump at home, take a photo and note its size and the date.
Book an examination for a new lump, especially if it grows, becomes sore, changes shape or sits where it bothers your dog. Rapid growth does not automatically mean cancer, but an early diagnosis makes it easier to choose the right treatment if the lump needs to be removed.