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. California has 1,026 practicing oncologists. Broken out by city, oncology doctor density in Anaheim is 13, in Apple Valley is 1, in Arcadia is 5, in Bakersfield is 9, in Berkeley is 14, in Beverly Hills is 17, in Burbank is 10, in Camarillo is 1, in Campbell is 9, in Chico is 3, in Chula Vista is 12, in Concord is 7, in Corona is 11, in Coronado is 4, in Covina is 3, in Duarte is 52, in Encinitas is 8, in Escondido is 8, in Eureka is 3, in Fairfield is 7, in Folsom is 5, in Fountain Valley is 18, in Fremont is 6, in Fresno is 20, in Fullerton is 6, in Gardena is 2, in Gilroy is 3, in Glendale is 16, in Glendora is 10, in Grass Valley is 1, in Hawthorne is 3, in Hemet is 4, in Huntington Beach is 10, in Irvine is 10, in La Mesa is 7, in Laguna Hills is 7, in Lancaster is 5, in Loma Linda is 14, in Lompoc is 2, in Long Beach is 25, in Los Alamitos is 10, in Los Angeles is 150, in Los Gatos is 2, in Manteca is 2, in Mission Viejo is 6, in Modesto is 5, in Montebello is 7, in Monterey is 3, in Monterey Park is 10, in Mountain View is 5, in Newport Beach is 18, in Oakland is 18, in Oceanside is 4, in Orange is 29, in Oxnard is 9, in Palm Springs is 7, in Palo Alto is 46, in Pasadena is 21, in Pleasanton is 10, in Pomona is 12, in Poway is 2, in Rancho Cucamonga is 5, in Rancho Mirage is 12, in Redding is 4, in Redondo Beach is 6, in Redwood City is 6, in Riverside is 12, in Roseville is 12, in Sacramento is 51, in Salinas is 6, in San Bernardino is 4, in San Diego is 59, in San Francisco is 73, in San Gabriel is 7, in San Jose is 16, in San Leandro is 5, in San Luis Obispo is 4, in San Mateo is 8, in San Ramon is 4, in Santa Ana is 1, in Santa Barbara is 10, in Santa Maria is 4, in Santa Monica is 31, in Santa Rosa is 11, in Sebastopol is 1, in Simi Valley is 5, in Sonora is 2, in Stockton is 5, in Sunnyvale is 3, in Thousand Oaks is 6, in Torrance is 22, in Upland is 4, in Vallejo is 8, in Victorville is 1, in Visalia is 3, in Vista is 8, in Walnut Creek is 20, in West Covina is 6, in Westlake Village is 3, and in Whittier is 7.

California’s population is 36,142,137, and it is America’s third largest and most populous state. It also claims the highest and lowest altitudes in the lower 48 states. The lowest point in the country, Death Valley, is also home to the nation’s highest recorded temperature, 134 degrees. Tourists flock to this state for its many outdoor activities and attractions, including Universal Studios, Disneyland, Rodeo Drive shopping, the Golden Gate Bridge in San Francisco, wine country tours, and California’s numerous beaches and parks. Los Angeles is the nation’s second largest city, but California’s capital is Sacramento. The giant sequoias in California’s forests are among the oldest living things in the world, and a redwood in the Redwood National Park is said to be the world’s tallest tree, at 365 feet. California achieved statehood in 1850, and was named the Golden State after the beginning of the Gold Rush in 1848.

According to 2005 Census estimates, California has a population of 36,132,147. Of this population, 9,308,563 are under the age of 18 and 3,827,038 are at or above the age of 65.