I don't think it is cancer. It is most probably saliva(mucous) extra-vasation into the tissue under the tongue causing a mucous retention cyst or 'ranula'
These mucoceles and ranulas tend to be relatively painless or asymptomatic lesions with little or no associated morbidity or mortality. Ranulas usually occur in children and young adults. Individuals with an oral ranula may complain of swelling of the floor of the mouth that is usually painless. The mass may interfere with speech, mastication, respiration, and swallowing because of the upward and medial displacement of the tongue. Oral ranulas may affect swallowing, speech, mastication, or respiratory function if they are large.
Please see your dentist or doctor to get a proper diagnosis and treatment. Do let us know how you get on.