Other issues thought to play a role in the spread of cancer include viruses, immune system issues, genetics, environment and age.

Other possible factors may include genetics and lack of outdoor activity.

Examples of limitations include genetics, culture, and many other factors.

Contributing factors may include genetics, infections, ultraviolet light, extreme stress, and the use of certain drugs.

These may include genetics (traits that run in families), environmental, and medical conditions.

Causes may include genetics, brain defects or injuries, an abusive environment, and others.

Factors suspected of causing migraines include genetics and being overweight.

They include genetics, diet and the social and physical environments.

These include caste systems, genetics and the defence of home territories.