Nine year old nephew, who is extremely fair complected, has recently developed l blood blister on his lower lip. It continues to enlarge and is now purple in color. He bumped it a few days ago,  he bumped it and it bled profusely. He was taken to the local ER, and was told it was from biting his lip (which he doesnt do) and it should dissipate in time. Despite the physicians prognosis, it has continued to grow in size and has begun to take on an irregular shape.It may be of importance to note that skin cancer is prevalent on his mothers side, and his father passed away at 31 of lymphoma. Could this lump be cancerous? He did spend a great deal of time in the sun this summer. Should I suggest they take him to a dermatologist? Can it be removed?
Biting is one of the differential diagnosis for a blister on lip in a 9yr child.it should heal in a matter of 1-2 weeks completely. As u said it started as an enlarging blister with bleeding and grown in size in an irregular shape, so the child should undergo biopsy to rule out malignancy. As family history also suggestive of cancer in the mother, you need to consult dermatologist or pediatric surgeon for biopsy and to proceed further.