Skin lymphoma (also known as cutaneous lymphoma) is a rare form of skin cancer that is not linked to sun exposure. There are several types of skin lymphoma and, as a category, they are rare, affecting about 6 in 1 million people. Yale Medicine is an internationally recognized center of expertise in diagnosing and treating skin lymphomas that range from early-stage to complex disease.

Skin lymphoma is a group of rare, usually slow-growing skin cancers that start in lymphocytes, which are a kind of white blood cell. While most lymphocytes are in lymph nodes, a key part of the body’s immune system, they are also present in the skin. When skin lymphocyte cells become damaged and grow uncontrollably, cancer can develop. Skin lymphomas typically present as a visible rash or as growths on the skin.

Broadly, there are two types of skin lymphomas: B-cell lymphomas and T-cell lymphomas (B cells and T cells are subtypes of lymphocytes). B-cell and T-cell skin lymphomas behave differently.

Doctors don’t know what causes skin lymphomas. They aren’t associated with any viruses, nor is there a genetic link. But there are some recognized risk factors, including:

• Age: Generally, skin lymphomas appear in older adults. But they also affect middle-age and younger people, including children.
• Race: There is a higher incidence among African-Americans of the most common type of T-cell skin lymphoma: mycosis fungoides.
• Sex: Most types of skin lymphoma are more likely to strike men than women.
• Damaged immune system:  People with weakened immune systems, or who are receiving treatments that weaken it, are at higher risk.

The symptoms of a skin lymphoma depend on whether it’s a T-cell or B-cell lymphoma.

Patients with T-cell lymphomas generally have flat rashes called patches or plaques. The rash may start in a small area and then extend over large areas of the body. The patches may be red, itchy and dry, and cracks may form in the skin. 

Other symptoms include fatigue, elevated white blood cell count and enlarged lymph nodes. In severe cases, T-cell lymphomas may cause disfiguring tumors to grow out of the skin.

B-cell lymphomas typically show up on the skin as raised, solid, nodular lesions, usually pimple-sized or larger.

Diagnosing skin lymphoma can be tricky because it’s easily confused with other, noncancerous, dermatologic conditions that cause similar symptoms. Diagnosis is also difficult because skin lymphomas usually grow slowly. 

“Typically, a patient may have something on his or her skin for several years before it’s properly diagnosed,” says Lynn Wilson, MD, MPH, clinical director of Therapeutic Radiology at Yale Medicine. “They may think it’s a bug bite, or they may think it’s an irritation or an allergic reaction, and it doesn’t really bother them that much.”

 Often, Dr. Wilson says, it’s not until standard skin treatments fail that lymphoma is suspected.

To obtain a proper diagnosis, you're likely to be seen first by a dermatologist, who examines the skin. Next, the dermatologist performs a skin biopsy, a simple procedure done in the office in which a sample of skin tissue is removed. The biopsy is then analyzed by a pathologist, a specialist who determines whether cells from the sample are malignant, and what kind of cells they are.

Because skin lymphomas are rare, they can be particularly hard to diagnose and classify. Biopsies may be sent to a major medical center that has specific and extensive expertise in diagnosing the condition. Yale Medicine is one such center. “We have dermatopathologists who are pathologists specializing in skin pathology,” Dr. Wilson says. “And they’re very subspecialized. They are very good at determining what is skin lymphoma and what isn’t.”

Yale Medicine has been an international center of expertise in skin lymphomas for several decades. The team at Yale Medicine is skilled at treating difficult advanced cases of lymphoma and early-stage cases.

Each patient is treated by a multidisciplinary team that collaborates to devise the most effective treatment plan. “We're very thoughtful about thinking of the patient as a whole person,” Dr. Wilson says, “and considering logistically what's easiest for them and their families.”