To dream of represents the freedom to think, make choices, or express yourself. It may also symbolize an ability to take your time. Any problems with your lungs may reflect feelings of being suffocated emotionally, being unable to express yourself, or having to rush.
To dream of cancer represents a situation that is slowly restricting freedom, choice, or your ability to express yourself. You may also feel that a situation is slowly restricting your ability to relax.
Example: A woman dreamed of having cancer. In real life the woman’s daughter was close to getting married and she strongly believed her daughter was too young.