Dreams are symbolic and not literal -- most of the time. Cancer tumors in dreams represent a variety of unprocessed psychological and emotional materials that the dreamer may be obsessing on. They represent all of those things that bother, disturb, anger, or hurt us and that we never directly deal with or let go of.
The dreamer’s mental, psychic or emotional problems may be proliferating and infecting many areas of thought and function. You may be experiencing anxiety and fear as a result of a bad habit or a certain situation in your daily life. However, if you are very worried and cannot get it out of your mind, go for a physical. When is the last time you did that anyway? In more superstitious interpretations, dreaming of cancer may be considered a dream of the contrary, but also of warning!... The Bedside Dream Dictionary
Fear of this illness, a part of our personality or being which is out of harmony with our wholeness; expression of how we feel about other people’s—especially our mother’s— emotional influence. This influence might be eating away at our own sense of well-being. Occasionally awareness of illness in part of body suggested. ... A Guide to Dreams and Sleep Experiences
1- Cancer is one of the prime fears that a human being has to deal with, so to dream of a cancer indicates we are out of harmony with our body. It indicates fear of illness and equally can represent something ‘eating away’ at us usually a negative idea or concept.
2- Intellectually we may have worked through our fears but still be left with attitudes and beliefs that cannot be cleared away. Very often this appears as cancer in dreams.
3- The Mother, the Moon and the astrological sign of Cancer.... Ten Thousand Dream Dictionary
To dream of cancer suggests something is eating away at us. That something we are ignoring or not attending to is gradually devouring all that is positive in us.... Dream Meanings and Dream Interpretation
Dreams of cancer represent unexpressed emotions, guilt, anger, resentment and a deep fear of the repercussions of fully expressing your feelings. You may be allowing guilt to eat away at you. Astrologically, Cancer represents sensitivity, empathy, and one who puts their imagination to use. This dream may be guiding you to spend time with people who understand, love and nurture you. Set boundaries, but be cautious of too much armor. See Aids, Sick and Disease.... Strangest Dream Explanations
Psychological / emotional perspective: Intellectually we may have worked through our fears but still be left with attitudes and beliefs that cannot be cleared away. Very often this appears as cancer or illness in dreams and equally can represent something ‘eating away’ at us – usually a negative idea or concept.... Dream Meanings of Versatile
Material aspects: Cancer is one of the prime fears that a human being has to deal with, so to dream of a cancer indicates we are out of harmony with our body. It also indicates fear of illness.... Dream Meanings of Versatile
Gives gender - specific: Since the astrological sign of cancer represents a feminine attribute, in a woman’s dream she may be considering her ability to nurture. In a man’s dream his focus may be on his attitude to his mother or mothering.... Dream Meanings of Versatile
The sign of the crab is an emotionally nurturing astrological sign.
The crab’s appearance may announce that a nurturing and caring individual has come your way or signify a need to make your home a more comfortable place. Finally, Cancer, the Crab, may be a warning sign that you are becoming a mother hen.... Ariadne's Book of Dream