Various causes of cancer are:-
Genetic mutations  Harmful rays due to exposure to sun/ radiation Diet and physical activity Hereditary Environmental factors

Symptoms of cancer, are usually caused by the effect of cancer on the part of body where it is growing. Although symptoms of cancer may appear in the form of general debility including weight loss or tiredness, yet it is generally advised that if anyone is experiencing unusual symptoms for more than a few weeks than he/she should seek medical attention.
Local symptoms: Local symptoms generally occur due to the mass of tumour or its ulceration. For example:-
Esophageal cancer can cause narrowing of the esophagus, making it difficult or painful to swallow, Colorectal cancer may lead to narrowing or blockages in the bowel, resulting in changes in bowel habits.
Systemic symptoms: General symptoms occur due to distant effects of the cancer that are not related to direct or metastatic spread. These may include:-
Unintentional weight loss Fever Getting extremely tired easily (Fatigue)

Remedial treatment: Remedial treatment refers to treatment which seeks to make the patient feel better and may or may not be combined with an attempt to attack the cancer. Treatment includes action to reduce the physical, emotional, spiritual, and psycho-social agony experienced by people with cancer.
Surgery: Surgery is the fundamental method of treatment of most isolated cancers and may play a role in remedial measure and prolongation of survival. Biopsy is normally required. It is typically an important part of establishing the definitive diagnosis and staging the tumour required. Localized cancer surgery typically attempts to remove the entire mass along with the lymph nodes in the region (in some cases).
Radiation: Radiation therapy involves the use of ionizing radiation in an attempt to either cure or ameliorate the symptoms of cancer. It is used in about half of the cases and can be either from internal sources in the form of brachytherapy or external therapy.
Chemotherapy: Chemotherapy in addition to surgery has proven to be useful in a number of different cancer types including: breast cancer, colorectal cancer, pancreatic cancer, osteogenic sarcoma, testicular cancer, ovarian cancer, and some lung cancers.

Cancers can generally be recognized by appearance of signs and symptoms through screening.

Cancers are classified based on the nature of cells that the tumor cells resemble and are therefore classified as:-
Carcinoma: Cancers that are derived from epithelial cells are known as carcinomas. This group of cancer is most common, especially in the older people, and includes nearly all cancers developing in the breast, prostate, lung, pancreas, and colon.
Sarcoma: These cancers are derived from connective tissues (i.e. bone, cartilage, fat), each of which develop from cells originating in mesenchymal cells outside the bone marrow.
Lymphoma and leukemia: These two classes of cancer arise from hematopoietic (blood-forming) cells that leave the marrow and tend to mature in the lymph nodes and blood, respectively. Leukemia is the most common type of cancer in children.
Germ cell tumor: Cancers derived from pluripotent cells ( refers to a stem cell that has the potential to differentiate into any of the three germ layers, endoderm (interior stomach lining, gastrointestinal tract, lungs), mesoderm (muscle, bone, blood, urogenital), and ectoderm (epidermal tissues and nervous system), most often presenting in the testicle or the ovary (seminoma).

http://www.cancer.orgNational Institute of Cancer  Prevention and Research (NICPR)www.who.intwww.iarc.fr