These factors include:

Possible harms from the screening test: for example, X-ray images involve exposure to potentially harmful ionizing radiation
The likelihood of the test correctly identifying cancer
The likelihood that cancer is present: Screening is not normally useful for rare cancers. Possible harms from follow-up procedures
Whether suitable treatment is available
Whether early detection improves treatment outcomes
Whether the cancer will ever need treatment
Whether the test is acceptable to the people: If a screening test is too burdensome (for example, extremely painful), then people will refuse to participate. Cost

Recommendations
U.S. Preventive Services Task Force
The U.S. Preventive Services Task Force (USPSTF) issues recommendations for various cancers:

Strongly recommends cervical cancer screening in women who are sexually active and have a cervix at least until the age of 65. Recommend that Americans be screened for colorectal cancer via fecal occult blood testing, sigmoidoscopy, or colonoscopy starting at age 50 until age 75. Evidence is insufficient to recommend for or against screening for skin cancer, oral cancer, lung cancer, or prostate cancer in men under 75. Routine screening is not recommended for bladder cancer, testicular cancer, ovarian cancer, pancreatic cancer, or prostate cancer. Recommends mammography for breast cancer screening every two years from ages 50–74, but does not recommend either breast self-examination or clinical breast examination. A 2013 Cochrane review concluded that breast cancer screening by mammography had no effect in reducing mortality because of overdiagnosis and overtreatment. Japan
Screens for gastric cancer using photofluorography due to the high incidence there. Genetic testing
Genetic testing for individuals at high-risk of certain cancers is recommended by unofficial groups.
Epigenetics
The classical view of cancer is a set of diseases driven by progressive genetic abnormalities that include mutations in tumor-suppressor genes and oncogenes, and in chromosomal abnormalities. A role for epigenetic alterations was identified in the early 21st century.Epigenetic alterations are functionally relevant modifications to the genome that do not change the nucleotide sequence. Examples of such modifications are changes in DNA methylation (hypermethylation and hypomethylation), histone modification and changes in chromosomal architecture (caused by inappropriate expression of proteins such as HMGA2 or HMGA1). Each of these alterations regulates gene expression without altering the underlying DNA sequence. These changes may remain through cell divisions, endure for multiple generations, and can be considered as equivalent to mutations. Epigenetic alterations occur frequently in cancers. As an example, one study listed protein coding genes that were frequently altered in their methylation in association with colon cancer. These included 147 hypermethylated and 27 hypomethylated genes. Of the hypermethylated genes, 10 were hypermethylated in 100% of colon cancers and many others were hypermethylated in more than 50% of colon cancers.While epigenetic alterations are found in cancers, the epigenetic alterations in DNA repair genes, causing reduced expression of DNA repair proteins, may be of particular importance. Such alterations may occur early in progression to cancer and are a possible cause of the genetic instability characteristic of cancers.Reduced expression of DNA repair genes disrupts DNA repair. This is shown in the figure at the 4th level from the top.