All types of leukaemia can present with oral manifestations, including swollen and painful gums, especially in acute leukaemia. However, it is not straightforward to define swollen gums as a precursor to leukaemia or any other cancer, only that they may be caused by leukaemia.
The exact type of cancer or what systemic disease the swollen gums mean will need to be clarified by a thorough examination in the relevant hospital department.