Retinoids are substances that help regulate the work of genes as cells grow and divide. Chemically related to vitamin A, retinoids are used to treat a wide variety of conditions and diseases, including several cancers.

Retinoids have been shown to be effective in reducing the risk of some cancers or in reducing the risk of a recurrence of cancer. These medications have been approved by the U.S. Food and Drug Administration (FDA) for use in the treatment of certain cancers, particularly skin cancers. They are usually administered in a topical gel or orally, depending on the condition being treated.

The National Cancer Institute is studying retinoids for their potential in preventing or treating other types of cancer, such as breast, bladder and liver cancers. There have been numerous clinical trials examining the effectiveness of retinoids as treatment for these cancers, as well as certain childhood cancers. However, retinoids can be associated with serious side effects, including a high risk of birth defects when used by pregnant women. More research is necessary to determine what role retinoids can play in the prevention and treatment of other types of cancers.

Retinoids are chemically related to vitamin A and occur naturally within the body. Their role is to regulate the work of genes, helping cells to mature and divide. As a synthetic drug, retinoids have been shown to induce cancer cells to “self-destruct” by a process called apoptosis (programmed cell death). This type of cell death is a controlled sequence of events that eliminates cells in such a way as to avoid the release of harmful substances into the surrounding area.

Retinoids have been approved by the U.S. Food and Drug Administration (FDA) for cancer treatment, including Kaposi’s sarcoma and cutaneous T-cell lymphoma. It is being studied for several other applications, such as treating malignant and premalignant skin cancers, including basal cell carcinoma and squamous cell carcinoma.

The National Cancer Institute (NCI) is studying retinoids as part of its research into chemoprevention. Chemoprevention uses natural or synthetic substances to reduce the risk of cancer or the possibility of a recurrence. Retinoids may be able to prevent abnormal cell growths, or dysplasias, from developing into cancer. Because they are related to or derived from vitamin A, retinoids have an antioxidant effect. Antioxidants are substances that may protect cells from the damage caused by unstable molecules known as free radicals. Damage caused by free radicals may lead to cancer.

Retinoids are being studied to determine their ability to treat and prevent numerous cancers, including cancers of the head and neck, breast, lung and prostate. 

Retinoid therapy can cause significant side effects, including the risk of birth defects. In addition, it is important for patients who take retinoids to not give blood during treatment or for three years after discontinuing retinoid therapy to prevent a pregnant woman from receiving retinoid–tainted blood.

Retinoids come in several forms and use will vary depending on the condition. They are administered according to the condition that is being treated. For example, many retinoids are available in a topical gel, which is commonly used to treat severe acne, leukoplakia and Kaposi’s sarcoma. Retinoids taken orally have been used to treat basal cell carcinoma, basal cell nevus syndrome and xeroderma pigmentosa, a rare genetic defect that affects the skin. Retinoid dosage depends on the particular medication and condition. As with all medications, it is important that a patient receive directions by their physician and/or pharmacist prior to starting any retinoid therapy.

There are several different types of retinoids. They are often referred to as antioxidant supplements used in chemoprevention (preventing cellular progression to cancer). Based on the condition or disease, retinoids can be used alone or in combination with other substances, such as beta-carotene or chemotherapy drugs.

Acne, psoriasis and other skin conditions are commonly treated with retinoids. These medications are used to treat some cancers and precancerous conditions, and there are clinical studies investigating additional use of retinoids with cancer. Retinoids have been used on:

• Actinic keratosis of the face
  
  
• Malignant skin cancers, including basal cell and squamous cell carcinoma
  
  
• Basal cell nevus syndrome
  
  
• Breast cancer
  
  
• Hodgkin’s and T-cell lymphoma
  
  
• Kaposi’s sarcoma
  
  
• Leukoplakia (a common condition characterized by white patches in the mouth)
  
  
• Lung cancer
  
  
• Oropharyngeal cancer
  
  
• Pediatric neuroblastoma and medulloblastoma
  
  
• Xeroderma pigmentosa (a rare skin condition that increases risk of skin cancers)

Retinoids can cause serious side effects. Therefore, patients with any of the following conditions should consult their physician prior to using retinoids:

• Lymphedema (swelling of arm or leg)
• Severe liver or kidney disease
• Heart disease
• Diabetes
• Bone marrow depression
• Infection
• Cataracts
• Herpes zoster (shingles)
• A condition involving phototherapy (therapeutic exposure to light)

Patients should be sure to discuss their complete medical history with the prescribing physician, including any drug allergies that may rule out retinoid therapy.

Some retinoids can have serious side effects. Precautions include avoiding use during pregnancy and avoiding direct sunlight and exposure to artificial ultraviolet light. Possible side effects include:

• Decreased HDL (“good”) cholesterol or increased LDL (“bad”) cholesterol
• Dry mouth with chapped lips
• Eye irritation or inflammation, including crusting of the eyelids
• Increased sensitivity to sunlight
• Increased toxicity of insect repellent DEET
• Intense redness
• Low thyroid function
• Severe birth defects if taken during pregnancy
• Skin scaling, peeling and dryness
• Swelling of the arms, feet hands or legs

Less common side effects with retinoid therapy include:

• Pain in the lower back, side or abdomen
• Bone spurs
• Runny nose, cough or hoarseness
• Diarrhea
• Difficulty sleeping
• Headache or dizziness
• Taste changes, excessive thirst or loss of appetite 
• Painful or difficult urination
• Pancreatitis (inflammation of the pancreas)
• Vision changes, including cataracts
• Weight gain
• Yellowing of the skin or eyes

Patients taking retinoid medications who experience these symptoms should contact their pharmacist or prescribing physician immediately.

Patients should consult their physician before taking any additional prescriptions, over-the-counter medications, nutritional supplements or herbal medications. Certain medicines can interact with other drugs or drug products.

Alcohol consumption is not advised while taking certain forms of retinoids. Individuals are advised to discuss the use of retinoids with their physician for possible restrictions and potential drug interactions.

Symptoms of overdose can be similar to the medication’s side effects, but are usually more severe. Patients exhibiting these symptoms should contact their physician immediately:

• Severe headache
• Nausea
• Vomiting
• Drowsiness
• Irritability
• Loss of balance
• Itching

Certain forms of retinoids have been proven to cause severe birth defects when taken by pregnant women or by the mother or father at the time of conception. Patients who plan to become pregnant or think they may be pregnant should contact the prescribing physician immediately. Retinoids should not be used in women who are breastfeeding. Also, a woman should not become pregnant for at least three years after discontinuing the use of certain retinoids.

Some retinoids require that patients register to monitor their use and to ensure that pregnancy is avoided. Two forms of effective birth control should be employed when taking retinoids. The “mini” birth control pill that contains no estrogen is not considered effective while on this type of medication. Taking other oral birth control pills should be discussed with a physician prior to starting retinoid therapy.

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about retinoids:

1. Can my type of cancer be treated with retinoids?
   
   
2. Which type of retinoid is best for me?
   
   
3. Is the retinoid FDA-approved for my cancer?
   
   
4. If not, how long will I be enrolled in a clinical trial for the drug?
   
   
5. How will retinoids affect my other cancer treatments?
   
   
6. How long can I expect to be on the medication?
   
   
7. What are the side effects of the retinoid I will be using?
   
   
8. Will retinoids have any long-term consequences after I stop using the drugs?
   
   
9. What should I avoid while on this medication?
   
   
10. When should I seek medical help if I am having a reaction to the medication?
    
    
11. Can I use any retinoids if I am trying to become pregnant?
    
    
12. What are the restrictions with the use of retinoids?
    
    
13. How will I know if the treatment is successful?
    
    
14. How will my condition be monitored in treatment?