What are the main symptoms of cancer==weight loss, anemia?

Depends on Cancer: The symptoms (sx) of cancer depend on the cancer type, stage, extent of disease, individual person, & treatment (etc). Some cancers are asx & may be observed (eg, cll). While others may be highly sx (shortness of breath in lung cancer or GI bleeding in colon cancer) & require multi-modality (surgery, chemo, radiation, etc) treatment. Some "cancer" sx are present in other diseases as well.

Depends: Early cancer may be asymptomtic. Depending on the site of cancer, there may be pain, change in bowel habits, cough and expectoration, palpable mass, blood in urine, vaginal discharge etc. Weight loss and anemia ususally come later.