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Normally, you probably hear health care professionals talk about ultraviolet (UV) light regarding sun safety.  

That¡¯s because exposure to the sun¡¯s UV light is connected to so many different types of skin cancer, including: 

• basal cell carcinoma
• squamous cell carcinoma
• melanoma

But did you know that UV light can sometimes be used to treat cancer or its side effects, rather than cause it? We spoke with stem cell transplant specialist , and dermatologist , to learn more. Here¡¯s what they shared. 

UV light therapy can be an effective cancer treatment 

As it turns out, UV light¡¯s ability to damage cells is precisely what makes it useful in cancer treatment.  

Some forms of UV light can be used to treat a form of cutaneous T cell lymphoma called mycosis fungoides. It can also help manage skin rashes caused by cancer treatments, allowing patients to stay on them for longer. 

¡°It may sound counterintuitive,¡± Huen says, ¡°but UV light can actually be helpful. A lot of patients do very well on it. It¡¯s a very effective treatment.¡±  

So, how does it work? 

Option 1: Using UV light ¡®indirectly¡¯

Let¡¯s take a look at extracorporeal photopheresis first. This process uses a special chemical to sensitize certain immune cells to the DNA-damaging effects of ultraviolet light. It¡¯s the same principle as chemoradiation, which uses chemotherapy to sensitize cancer cells to the effects of radiation therapy. 

The main difference is that while chemoradiation is applied directly to the body, extracorporeal photopheresis takes place entirely outside of it.  

¡°Extracorporeal photopheresis does not expose you directly to UV light,¡± explains Hosing.  

Instead, your blood is drawn into a special apheresis machine, injected with a photosensitive agent called 8-methoxypsoralen (8-MOP), and exposed to a concentrated dose of UV light before being returned to your circulatory system. 

¡°This modulates the function of immune cells so that they cannot keep causing inflammation,¡± adds Hosing.   

The uses of extracorporeal photopheresis

The Food and Drug Administration (FDA) approved both the extracorporeal photopheresis device and the sensitizing agent for treating various conditions and side effects in 1988. Currently, it is used to treat: 

• an aggressive subtype of cutaneous T cell lymphoma called S¨¦zary syndrome  
• graft vs. host disease (GVHD) in allogeneic stem cell transplant recipients  
• solid organ transplant rejections in patients who¡¯ve received donated hearts or lungs 

¡°There have been some clinical trials testing extracorporeal photopheresis for the treatment of other skin conditions, too, such as vitiligo (a condition that causes blotchy skin) and atopic dermatitis,¡± notes Hosing. ¡°But none of those have really panned out.¡± 

Option 2: Using direct UV light exposure

Surprisingly, patients with a form of cutaneous T cell lymphoma called mycosis fungoides are sometimes asked to expose the affected skin to direct sunlight or a UV lamp. The latter is a practice known as phototherapy or ¡°box therapy.¡±  

¡°Doctors sometimes tell their patients to sit outside for 20-30 minutes a day, with the affected skin exposed,¡± explains Hosing. ¡°That¡¯s considered helpful when the disease is minimal and limited to small areas. But if you have S¨¦zary syndrome and it involves the blood, then you¡¯ll need systemic treatment. Just exposing the surface of the skin to UV light won¡¯t be enough.¡± 

The uses of phototherapy

Phototherapy is sometimes administered in a doctor¡¯s office when patients are unable to reliably expose their skin to the sun. It is sometimes called ¡°box therapy¡± because patients must stand or lie naked inside a special windowless chamber to receive the UV light therapy. But don¡¯t be confused if you go in for treatment one day and think that the ¡°box¡± looks just like a tanning booth. 

¡°While the devices might look similar, they are not the same thing,¡± explains Huen. ¡°The machines at tanning salons are not well-supervised and not designed for medical use. In a doctor¡¯s office, patients receive a controlled dose of the safest wavelength of light, gradually adjusted to their specific needs.¡± 

In addition to mycosis fungoides, phototherapy is used to treat: 

• dermatitis 
• psoriasis 
• eczema 
• rashes caused by targeted therapy or immunotherapy  

¡°Obviously, it might not be the best choice if someone has had melanoma or skin cancer,¡± Huen explains. ¡°But if you¡¯re being treated for a totally different type of cancer and struggling with severe skin-based side effects, this might offer you just enough relief to continue with systemic therapy.¡± 

The best candidates for phototherapy

Not every person with a qualifying condition will be a good candidate for phototherapy. 

¡°This also wouldn¡¯t be the best choice if you¡¯ve only got one tiny little spot on your hand,¡± notes Huen. ¡°At least 10-20% of your skin must be affected. Rashes and other skin conditions have to be pretty extensive and not be getting any better with creams or lotions in order to justify full-body exposure.¡± 

Phototherapy can also be used to help patients avoid or delay systemic therapy for cutaneous T cell lymphoma ¡ª and the side effects that come with it. 

¡°Since phototherapy is applied directly to the skin, it has few side effects,¡± Huen explains. ¡°That allows some patients to delay systemic treatment indefinitely.¡± 

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