Cancer is caused by certain changes to genes that control the way our cells function, especially how they grow and divide. Some people have inherited gene faults that increase their risk of developing certain types of cancer. In this article, we touch on five of the more common inherited cancers. In part two of this article we’ll share the 6th through 10th most common inherited cancers.
5 to 10% of all cancers are caused by inherited genes
Inherited genetic mutations play a significant role in the development of about 5 to 10% of all cancers. Researchers have associated mutations in specific genes with more than 50 hereditary cancer syndromes (we touch on 10 in this series), which are disorders that may predispose individuals to developing certain cancers.
Cancer-causing genetic changes can also be acquired during one’s lifetime as the result of errors that occur as cells divide or from exposure to substances such as certain chemicals in tobacco smoke, and radiation, like ultraviolet rays from the sun, that damage DNA. Genetic changes that occur after conception are called somatic (or acquired) changes.
If a close member of your family has had one or more of the types of cancer mentioned in these articles and you have concerns, see your physician to discuss your next steps. Tests are available for some gene faults, but not all of them.
1. Colorectal cancer
Colorectal (cancer that begins in the colon or rectum) cancer is the 4th most common type of cancer in the U.S. In 2017, 95,520 new cases of colon cancer and 39,910 new cases of rectal cancer are expected to be diagnosed.
The genetic fault
HNPCC, also known as Lynch syndrome is the most common form of hereditary colon cancer, accounting for about 3% of all colorectal cancer diagnoses each year. People with HNPCC often have at least three family members and two generations with colorectal cancer, and cancer develops before age 50. Although not everyone who inherits the HNPCC gene will develop colorectal cancer, the risk is very high — about 80%.
Familial Adenomatous Polyposis (FAP) Syndrome is a rare condition characterized by benign polyps in the large intestine and upper respiratory tract. If the colon is not surgically removed, there is almost a 100% chance that some of the polyps will develop into cancer, usually by age 40.
Peutz-Jeghers Syndrome – associated with polyps in the digestive tract and increased pigmentation of the face and hands is also associated with an increased risk in colorectal cancer.
Colonoscopy is the best screening tool for those at risk of inherited colorectal cancer. The American Cancer Society recommends men and women at average risk for developing colorectal cancer start screening at age 50. See the site for recommendations.
About five to 10% of all colorectal cancers are caused by a heritable mutation.
2. Breast cancer
Breast cancer has the distinction of being the most common form of cancer in the U.S. with 316,128 new diagnoses expected in 2017.
The genetic fault
Most inherited cases of breast cancer are associated with the BRCA1 (BReast CAncer gene one) and BRCA2 (BReast CAncer gene two) genes.
We all have BRCA1 and BRCA2 genes, which work to repair cell damage and keep breast, ovarian and other cells growing normally. When these genes contain mutations that are passed from generation to generation, the genes don't function normally and breast, ovarian, and other cancer risk increases. Women who have an abnormal BRCA1 or BRCA2 gene (or both) can have up to an 80% risk of being diagnosed with breast cancer during their lifetimes.
There are genetic tests available to determine if someone has an abnormal BRCA1 or BRCA2 gene. Those at high risk because of an abnormal breast cancer gene, should develop a screening plan with their physician that may include early and more frequent screenings, including: monthly breast self-exams, yearly breast exam by a doctor, annual mammograms, annual MRI scans.
About five to 10% of breast cancers are thought to be hereditary.
3. Kidney cancer (renal cell)
Kidney cancer is the 8th most common cancer in the U.S. About 63,990 new cases of kidney cancer (40,610 in men and 23,380 in women) will be diagnosed in 2017.
The genetic fault
The following four major autosomal dominantly inherited renal cell cancer syndromes have been identified: von Hippel-Lindau disease, hereditary leiomyomatosis, Birt-Hogg-Dubé syndrome, and hereditary papillary renal carcinoma. These pathogenic variants are estimated to account for only 5% to 8% of renal cell cancer cases overall.
It is likely that other undiscovered genes and background genetic factors contribute to the development of familial RCC in conjunction with non-genetic risk factors.
Genetic testing is available to identify if the genes are present. If they are, regular screening by a physician for both renal and non-renal manifestations of disease are warranted.
Inherited genetic abnormality accounts for about two in 100 kidney cancers (2%).
Melanoma is the 5th most common cancer in the U.S. with 87,110 new cases estimated for 2017. The main cause of melanoma is too much exposure to ultraviolet light, from sunlight or from artificial sources such as sun beds.
The genetic fault
Familial malignant melanoma is a term usually referring to families in which two or more first-degree relatives, such as a parent, sibling and/or child, have melanoma. To date, two genes have been primarily linked to familial melanoma — CDKN2A and CDK4. A mutation in one of these genes gives a person an increased risk of melanoma. However, alterations in these two genes only account for a small percentage of familial melanoma.
Genetic testing for mutations in the CDKN2A gene is commercially available. In families known or strongly suspected to have familial melanoma, thorough skin exams should initially be performed every three to six months and children should begin screening by age 10. Family members should also perform regular self-examinations to look for skin changes. Due to the high risk of multiple melanomas, people with familial melanoma should avoid sun exposure unprotected.
About one in 10 people (10%) who have melanoma have a strong family history of the disease.
5. Ovarian cancer
Ovarian cancer ranks fifth in cancer deaths among women. In 2017, there will be 22,440 estimated new cases.
The genetic fault
The faulty genes that are known to increase the risk of ovarian cancer are primarily the BRCA1 and BRCA2 genes.
Lynch syndrome — also called hereditary non-polyposis colorectal cancer, increases ovarian cancer, as well as uterine and colorectal cancer risk.
Peutz-Jeghers syndrome – associated with polyps in digestive tract and increased pigmentation of the face and hands is also associated with an increased risk in ovarian cancer.
Genetic tests can detect gene mutations associated with these inherited syndromes. When ovarian cancer is found early at a localized stage, about 94% of patients live longer than five years after diagnosis. Several large studies are in progress to learn the best ways to find ovarian cancer in its earliest stage. The two tests used most often to screen for ovarian cancer are transvaginal ultrasound (TVUS) and the CA-125 blood test.
About 10 to 15% of ovarian, fallopian tube and peritoneal cancers occur because of an inherited genetic mutation.
If you or a loved one are at risk for an inherited cancer and you want to explore next steps, first meet with your physician. Together you can develop a testing or screening plan that makes sense based on your risk factors.
For those facing a cancer diagnosis for an inherited or non-inherited cancer, compassionate, quality care is available from Dr. Perez and Sierra Nevada Cancer Center. With locations in Carson City, Stateline, Gardnerville and Fallon, the care you need is close by. To schedule an appointment, call (775) 883-3336.