Oncology is the study and treatment of cancer and tumors. An oncologist is a physician who diagnoses and treats cancer patients. The oncologist sometimes uses chemotherapy, and consults with other physicians to coordinate other methods of cancer treatments for a patient. Cancer patients need to take in to account the likelihood of a cure, or of prolonging life when cure is not possible, the effect of treatment on their symptoms, and the side effects of the treatment. People who are candidates for radiation therapy or anti-cancer drugs need to understand the risks involved with treatment. An oncologist can help to counsel a patient on treatment options and what to expect.

Physicians in this specialty treat patients suffering from numerous diseases and illnesses, but some of the most common are colon cancer, breast disease, Spinal Cord Tumors, Melanoma, Skin Cancer, breast cancer, Bone Marrow, Hodgkin's disease, lymphoma, Mesothelioma, Sarcoma, lung cancer, Leukemia, Pancreatic cancer, Cervical cancer, Liver cancer, Mesothelioma Cancer (Asbestos Cancer), Brain cancer, Acute myeloid leukemia, and bone cancer.

Once properly diagnosed, practitioners can perform numerous procedures on patients including Colonoscopy, breast reconstruction, Chemotherapy, Brachytherapy, cryosurgery, mastectomy, Cryotherapy, CABG, breast surgery, surgery, radiotherapy, Bone marrow transplantation (BMT), adjuvant therapy, monoclonal antibody treatments, External Beam Radiotherapy, Hormone manipulation, and immunotherapies.

To diagnose patients with possible illnesses and diseases, specialists will often perform one of many tests including biopsy, MRI scanning, Beta- HCG, CT scanning, X-rays, Magnetic Resonance Imaging (MRI), Computed Axial Tomography (CT or CAT Scan), ultrasound, endoscopy, NSE, CEA, Blood tests, CA 125, Tumor markers, Beta HCG, Positron emission tomography, Scintigraphy, PSA, and Alpha fetoprotein.

Doctor density varies by specialty and location. Illinois has 436 practicing oncologists. Broken out by city, oncology doctor density in Alton is 5, in Arlington Heights is 14, in Aurora is 5, in Belleville is 6, in Benton is 2, in Berwyn is 10, in Bloomingdale is 1, in Bloomington is 5, in Blue Island is 3, in Breese is 2, in Burbank is 2, in Carbondale is 3, in Carlinville is 2, in Centralia is 3, in Champaign is 5, in Chester is 3, in Chicago is 184, in Chicago Heights is 2, in Clinton is 2, in Danville is 2, in Darien is 3, in Decatur is 11, in Dekalb is 2, in Des Plaines is 3, in Dixon is 1, in Downers Grove is 3, in Edwardsville is 1, in Effingham is 8, in Eldorado is 1, in Elgin is 6, in Elmhurst is 10, in Eureka is 1, in Evanston is 21, in Evergreen Park is 1, in Fairfield is 2, in Flossmoor is 9, in Freeport is 10, in Galesburg is 3, in Geneva is 6, in Granite City is 2, in Gurnee is 3, in Harrisburg is 1, in Harvey is 5, in Hazel Crest is 2, in Herrin is 3, in Highland Park is 11, in Hinsdale is 7, in Jacksonville is 2, in Joliet is 16, in Kankakee is 6, in La Grange is 10, in Lake Forest is 6, in Lake Villa is 1, in Lansing is 1, in Lincoln is 2, in Litchfield is 1, in Lockport is 2, in Mahomet is 4, in Marion is 1, in Martinsville is 1, in Mattoon is 6, in Maywood is 17, in Mchenry is 9, in Moline is 6, in Morris is 5, in Mount Vernon is 3, in Naperville is 10, in Normal is 5, in Olympia Fields is 1, in Palos Heights is 7, in Pana is 1, in Paris is 1, in Park Ridge is 11, in Pekin is 1, in Peoria is 7, in Pinckneyville is 1, in Pittsfield is 1, in Quincy is 3, in Red Bud is 1, in River Forest is 2, in Rock Island is 1, in Rockford is 10, in Rolling Meadows is 3, in Salem is 1, in Sandwich is 3, in Silvis is 7, in Sparta is 4, in Springfield is 14, in Streator is 1, in Taylorville is 4, in Tinley Park is 12, in Urbana is 6, in Vandalia is 1, in Waterloo is 1, in Watseka is 2, in Waukegan is 1, in Wheaton is 2, in Winfield is 5, in Woodstock is 2, and in Yorkville is 5.

Most people think that Chicago, because of its size and popularity, is Illinois’ capital city, but that distinction belongs to Springfield, home of the Abraham Lincoln Museum. Illinois has hundreds of museums, numerous yearly art and ethnic festivals, a lakeshore bordering Lake Michigan, and the many national forests and parks that offers visitors camping, horseback riding, biking, kayaking, and fishing. Chicago is home to the Sears Tower, the Shedd Aquarium, the Art Institute of Chicago, the Adler Planetarium, the Museum of Science and Industry, and other cultural opportunities and restaurants in the Navy Pier area.

According to 2005 Census estimates, Illinois has a population of 12,763,371. Of this population, 3,172,677 are under the age of 18 and 1,523,937 are at or above the age of 65.