Fatigue is a symptom most commonly associated with the diagnosis of cancer. Fatigue often
appears before the diagnosis of cancer, is increasing during treatment with chemotherapy and
persists for years after treatment in more than 35% of patients. Fatigue is the earliest and
most important symptom described by cancer patients. Its prevalence in cancer chemotherapy
patients is between 70 and 100%. Fatigue is more common to cancer patients and to the general
population or other types of patients. Typically described as a lack of energy associated
with mental disorders, fatigue related to cancer can be extremely debilitating. The causes
are many, mainly including the cancer itself, side effects due to treatment, sleeplessness
due to pain, anxiety or depression. The cancer-related fatigue has a negative and significant
direct impact on all aspects of the patient's quality of life, especially the physical,
social and behavioral. Despite the availability of certain treatments and the advanced
biomedical research, fatigue remains an inevitable consequence of cancer and its treatment.
The therapeutic use of natural light in medicine dates back to the late nineteenth century.
Its remarkable effect on the stimulation of the immune system and fight against infections
caused the development of the first therapy techniques (also called luxthérapie) awarded in
1903 by the Nobel Prize in medicine and physiology. Light plays a fundamental role in the
regulation of circadian rhythms and homeostatic. The mechanism of action passes through a
path "non-visual" involving melanopsin ganglion cells located in the retina. Activation of
the pineal gland (epiphysis) by melanopsin cells allows transduce information "shadow and
light" in melatonin synthesis from serotonin. Today, the effectiveness of the therapy is well
established for treating fatigue-related disorders such as chronic fatigue, seasonal
depression or seasonal or non-certain sleep disorders and in which the melatonin metabolism
is disturbed. Light therapy, by its mechanism of action, allows reprogramming "of the
biological clock and improved synchronization of circadian rhythms.