The issues concerning the relationship Intranasal Light Therapy with cancer is multi-dimensional. Broadly, there is the issue of whether this therapy has inherent carcinogenic radiation risk, and what the positive outcomes are.
Malignancy risk and effect on tumors
Since low level laser therapy is known to stimulate cellular activity, an often asked question of concern is whether it will likewise stimulate malignant tumor cell growth. The short answer is no. The photons impacting the cells are of very low energy and generated out of wavelengths that are known to have non-significant catabolic values (even though they do excite the creation of low level free radicals). Wavelengths of the red spectrum used in Intranasal Light Therapy is far longer than the safety limit of 320 nm (shorter wavelengths have the potential of ionising tissue molecules and hence carcinogenic, as witnessed for ultraviolet light).
Will the light dosage stimulate a cancer tumor in the nasal cavity? Based on an animal study, it would instead be helpful. Experiments on rats show that small tumor exposed to laser therapy may recede and completely disappear.  The local immune system is probably more stimulated than the tumor. 
Treatments with Intranasal Light Therapy
The evidence supporting Intranasal Light Therapy for cancer appears stronger for prevention and post-conventional-therapy recovery/rehabilitation than for treatment. Let’s look at the evidence under the categories of 1. Prevention, 2. Alleviating cancer-related pain and fatigue 3. Post-cancer therapy recovery and rehabilitation.
The key to effective cancer prevention is the health of the immune system. Its importance for controlling and shaping developing tumors are well established. For this reason, the evidence supporting Intranasal Light Therapy to treat HIV/AIDS is relevant. Amongst the evidence, it is found that this this therapy proliferates white blood cells, the core of immune system health.  One category of these cells, the T cells are able to target body cells that have become malignant. This therapy would be effective in treating diseases caused by cancerous pathogens such as the hepatitis B and C viruses (liver cancer), human papilloma viruses (cervical, anal and genital cancers)and helicobacter pylori (stomach cancer).
It is widely accepted that persistent oxidants which contribute to oxidative stress is influential in creating malignancy. The stimulation of redox signalling as the biomechanism behind the efficacy of Intranasal Light Therapy leads to restoring the redox and oxidant/anti-oxidant balance (homeostasis). This suggests that Intranasal Light Therapy is a viable systemic method for cancer prevention, or at least in many cases.
2. Alleviating cancer-related pain and fatigue
The use of light therapy for treating cancer has been most effective in the form of “photodynamic therapy” (PDT). Intranasal light therapy has been found more effective in systemic relief of pain and cancer-related fatigue (CRF). Research by Li et al has found that low level intranasal laser therapy could elevate blood β endorphin, which relieves pain and produces a feeling of well-being. 
CRF is experienced during the course of metastasis as well as during chemo and radiation therapies. Intranasal Light Therapy stimulates cellular rehabilitation through various pathways. This restoration process contributes to improvement on fatigue caused by various sources, including CRF.
3. Post cancer therapy recovery and rehabilitation
One can be certain of the destruction of white blood cells during common cancer therapies such as chemo and radiation therapies. The above discussion supports Intranasal Light Therapy to combat chronic fatigue arising from this event. However, the destruction of critical white blood cells also means that the recovery stage is fraught with dangers of infection, with the body defenseless against a bacterial or viral infection. Intranasal Light Therapy would accelerate recovery during this rehabilitation because it is known to accelerate the proliferation of white blood cells for fighting the infections.
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Image by Salvatore Vuono