Primary cutaneous lymphoma (skin lymphoma): types, diagnosis and treatment in the UK

Lymphoma Action explains that lymphoma is a cancer that starts in white blood cells called lymphocytes, which are part of the immune system. Skin lymphomas, also called cutaneous lymphomas, develop when lymphocytes grow out of control in the skin. The word primary means the lymphoma started in the skin, rather than starting somewhere else, such as a lymph gland, and spreading to the skin. Lymphoma that starts elsewhere and spreads to the skin is not a skin lymphoma.

There are two kinds of lymphocyte, T cells and B cells, and skin lymphomas can develop from either. Cancer Research UK calls them cutaneous T cell lymphoma (CTCL) and cutaneous B cell lymphoma (CBCL). CTCL is the most common type of skin lymphoma and CBCL is more unusual.

Lymphoma Action describes skin lymphoma as a rare and complex condition and says that in most cases it does not affect life expectancy and is treated more like a chronic condition. That is reassuring but should be balanced with the fact that some types are fast growing and need prompt treatment, which is why the exact type matters.

The most common T-cell skin lymphoma is mycosis fungoides, which Cancer Research UK describes as a very slow growing type. The second most common is Sezary syndrome, in which Lymphoma Action says people have erythroderma, swollen lymph nodes and abnormal cells in the blood. Cancer Research UK describes Sezary syndrome as a faster growing, high grade type. There are other rarer T-cell skin lymphomas, and your specialist can say whether your subtype is usually slow or fast growing.

For B-cell skin lymphoma, Cancer Research UK names primary cutaneous follicle centre lymphoma, primary cutaneous marginal zone lymphoma and primary cutaneous diffuse large B-cell lymphoma, leg-type. It describes follicle centre lymphoma as a low grade type and the most common CBCL, with around 60 out of 100 CBCLs being this type.

Lymphoma Action says different types look quite different from one another, particularly early on. In mycosis fungoides, patches of dry, discoloured, usually red skin appear and can look like dermatitis, eczema or psoriasis. They tend to be dry, sometimes scaly and may be itchy, and are most common on the buttocks or torso but can occur anywhere. On Asian or black skin they may appear as patches of lighter or darker skin. Patches may thicken into plaques, which can be itchy and sometimes ulcerate, and in most people the lymphoma never develops beyond the patch and plaque stage.

Cancer Research UK says that with darker skin, patches may appear lighter or darker than the surrounding skin. Some people develop larger raised swellings called nodules or tumours, and later stage disease can cause generalised reddening (erythroderma).

B-cell skin lymphomas, according to Cancer Research UK, most often cause a small raised lump or lumps that can look like spots or pimples, which may become thicker and flatter plaques or larger nodules that are dark red or purple and can break down. Weight loss, fever or night sweats are described as rare. Lymphoma Action reminds readers not to be alarmed if their skin looks similar to the photographs it shows, because many more likely and less serious skin conditions can look the same.

Lymphoma Action says skin lymphoma is difficult to diagnose because it can develop slowly, sometimes over decades, and often resembles more common skin conditions, including eczema, psoriasis, lichen planus, lupus erythematosus, fungal infections and contact dermatitis. Some treatments for those conditions, such as steroid creams, can also help skin lymphoma for a while, which may delay suspicion. It says that on average it takes around three years to get a confirmed diagnosis, though it can be much more or less.

The most important test is a skin biopsy. A doctor or nurse numbs an area of skin with local anaesthetic and removes a small sample, which is examined under a microscope and sent for specialised genetic tests. Lymphoma Action says results can take 4 to 6 weeks and are often not clear-cut, so several biopsies over months or even years may be needed. Cancer Research UK likewise says it is not unusual to have more than one biopsy over weeks or months.

If lymphoma is diagnosed, further tests may include blood tests, a CT or PET-CT scan and a lymph node biopsy. Cancer Research UK adds that a team from several hospital departments, which might include a dermatologist, a haematologist and an oncologist, is involved in diagnosis and treatment. Lymphoma Action says a bone marrow biopsy is rarely performed in skin lymphoma.

Cancer Research UK explains that grade describes how quickly a lymphoma is likely to grow and spread, and stage shows how much skin is affected and whether it has spread to lymph nodes or other organs. For mycosis fungoides it describes four main stages. Stage 1 affects only the skin in patches or plaques, with stage 1A meaning less than 10% of the skin is affected and 1B meaning more than 10%. Stage 2 includes enlarged lymph nodes without cancerous cells (2A) or one or more lumps in the skin (2B). Stage 3 means most of the skin is red and sore, and stage 4 includes high numbers of cancerous T cells in the blood, cancerous cells in the lymph nodes or spread to organs such as the liver or spleen.

Your doctor may also mention a SWAT score, which measures how much skin is affected and is used to monitor the lymphoma. Cancer Research UK says this is different from the stage.

Lymphoma Action says many people with a slow-growing skin lymphoma do not need treatment straight away. Instead the doctor monitors the condition, an approach called active monitoring or watch and wait, which it says research and experience have shown to be the best approach for some types and stages. Cancer Research UK says that for stage 1 or 2A mycosis fungoides, starting treatment earlier will not affect your outlook or how fast it grows, and that early stage treatment is more about controlling symptoms. Lymphoma Action acknowledges that many people find active monitoring very difficult to cope with.

When treatment is needed, Lymphoma Action describes skin-directed treatments such as creams, lotions or ointments, light therapy and radiotherapy, and treatments that affect the whole body, such as immunotherapy, steroids, chemotherapy or, rarely, a stem cell transplant. People with a B-cell skin lymphoma affecting a single area may have surgery to remove it.

Cancer Research UK adds that for mycosis fungoides first treatments may include steroid or chemotherapy creams, phototherapy such as PUVA or narrow band UVB, and radiotherapy to small areas. Total skin electron beam therapy may be used in more advanced stages, and extracorporeal photopheresis for stage 3. It notes that mycosis fungoides can be controlled very well but that it is common for it to relapse, and that people often need more than one type of treatment over their lifetime.

Because skin lymphoma is usually long-term, the emotional side matters. Lymphoma Action says the time before diagnosis can be frustrating and anxious, and it also recognises that some people find it hard to come to terms with a result either way, including when a specialist concludes it is not lymphoma after all. If you are struggling, it suggests talking to your doctor or specialist nurse, who have helped others in the same position.

The NHS general guidance on non-Hodgkin lymphoma says you will have a clinical nurse specialist as your main point of contact, and that Macmillan Cancer Support runs a free helpline. These sources are for the wider group of lymphomas but are relevant to anyone under a cancer team.

Skin lymphoma is usually managed by a dermatology-led or haematology-led team, often at a specialist centre, and a local dermatologist may refer you there if the diagnosis is unclear. Private dermatology appointments can be used to speed up an initial opinion for a persistent rash, but the diagnosis still depends on biopsy and expert pathology review, and long-term treatment such as phototherapy or radiotherapy is typically delivered in specialist units. Keep copies of biopsy results so they can be reviewed by different teams.