What is Cutaneous T-Cell Lymphoma (CTCL)?

You went to the dermatologist for what looked like stubborn eczema. Months — sometimes years — later, the biopsy comes back with three words you weren’t prepared for: cutaneous T-cell lymphoma.

Most people have never heard of it. It’s rare, it mimics common skin conditions, and even doctors can miss it for a long time. But it’s a cancer, and right now it’s at the center of a national conversation about whether the drug Dupixent has been linked to it.

This guide breaks down what CTCL actually is, how it shows up, the main types you’ll hear about, how it’s treated, and why thousands of patients across the country are now asking whether their eczema medication played a role.

CTCL in One Sentence

Cutaneous T-cell lymphoma is a rare type of non-Hodgkin lymphoma in which a person’s T-cell lymphocytes — a kind of white blood cell that normally fights infection — become cancerous and accumulate in the skin.

Even though CTCL shows up on the skin, it’s not technically a “skin cancer” the way melanoma or basal cell carcinoma is. The mutated cells aren’t skin cells. They’re immune cells that have gone haywire and are using the skin as their primary home.

The annual incidence is roughly 0.5 per 100,000 people in the United States, according to data from the National Cancer Institute. Healthcare providers diagnose about 3,000 Americans with CTCL each year. It tends to affect adults over 50, men more often than women, and Black Americans more often than white Americans.

The Two Most Common Types of CTCL

Around 70–75% of CTCL cases fall into one of two diagnoses.

1. Mycosis Fungoides

Mycosis fungoides is the most common form of CTCL, accounting for roughly half of all primary cutaneous lymphomas worldwide. Despite the alarming name, it has nothing to do with fungus. Doctors named it in 1806 after the mushroom-shaped tumors that can develop in late-stage cases.

Mycosis fungoides is slow-growing. Many patients live with it for decades. It typically progresses through stages:

• Patch stage: Flat, scaly, discolored patches that look very much like eczema or psoriasis. Often on the trunk, buttocks, or other sun-protected areas.
• Plaque stage: Patches thicken and become raised, sometimes with intense itching.
• Tumor stage: Raised lumps form on the skin, sometimes ulcerating.
• Erythrodermic stage: Large areas of the body — sometimes nearly all of it — turn red, scaly, and inflamed.

Not every patient progresses through every stage. Many never advance beyond patches.

2. Sézary Syndrome

Sézary syndrome is the aggressive cousin of mycosis fungoides. It involves the same kind of cancerous T-cells, but they’ve spilled out of the skin and into the bloodstream and lymph nodes. It accounts for roughly 3–5% of CTCL cases.

Symptoms include:

• A widespread red, scaly, intensely itchy rash covering most of the body (called erythroderma)
• Skin that may peel or feel like a severe sunburn
• Swollen lymph nodes
• Thickening of the palms and soles
• Hair loss, eyelid retraction, and nail abnormalities in advanced cases
• Fatigue, weight loss, and fever

Mycosis fungoides can sometimes transform into Sézary syndrome over time. The cancerous cells circulating in the blood are called Sézary cells.

Less Common Types

A handful of rarer subtypes also fall under the CTCL umbrella, including primary cutaneous CD30-positive lymphoproliferative disorders (lymphomatoid papulosis and primary cutaneous anaplastic large cell lymphoma), subcutaneous panniculitis-like T-cell lymphoma, and a few others. These are vanishingly rare and typically require care at a specialized cancer center.

Why CTCL Is So Easy to Miss

The reason CTCL gets misdiagnosed for years — sometimes a decade or more — comes down to one fact: early CTCL looks almost identical to eczema, psoriasis, dermatitis, and other common rashes.

A typical mycosis fungoides patch:

• Itches
• Is dry and scaly
• Comes and goes
• Responds, at least partially, to steroid creams and other anti-inflammatory treatments

That description fits dozens of benign skin conditions. The Cleveland Clinic notes that mycosis fungoides may be present for years before a definitive diagnosis is made, and that biopsies in the early patch stage are often inconclusive — sometimes requiring repeat biopsies before pathologists can confirm the diagnosis.

This is exactly why CTCL becomes especially dangerous when a patient is on a strong anti-inflammatory medication. The drug can suppress the visible rash while the underlying cancer continues to evolve unseen.

How CTCL Is Diagnosed

There’s no single blood test that confirms CTCL. Diagnosis usually involves:

1. Skin biopsy. A pathologist examines a small piece of skin under a microscope, looking for the characteristic atypical T-cells that have invaded the upper layers of the skin (a feature called epidermotropism).
2. Immunohistochemistry. Special stains identify the markers on the cancerous cells (most CTCLs express CD3 and CD4 with loss of certain other markers).
3. T-cell receptor gene rearrangement testing. Molecular testing looks for monoclonal populations of T-cells, which is a hallmark of cancer.
4. Blood work. A “Sézary cell count” looks for cancerous T-cells circulating in the blood.
5. Imaging. CT or PET scans can identify swollen lymph nodes or organ involvement in more advanced disease.

Patients are then staged using a system that accounts for skin involvement, lymph node involvement, blood involvement, and any spread to internal organs.

How CTCL Is Treated

There’s no one-size-fits-all treatment, but options scale with the stage of disease:

Early Stage (Skin-Limited)

• Topical corticosteroids for patches and plaques
• Topical chemotherapy (mechlorethamine gel)
• Phototherapy — narrowband UVB or PUVA light treatments
• Topical retinoids

Intermediate or More Aggressive Disease

• Total skin electron beam therapy (TSEBT) — radiation delivered to the entire skin surface
• Localized radiation for tumor-stage lesions
• Systemic retinoids (bexarotene)
• Interferon-based therapies

Advanced Disease (Sézary Syndrome or Tumor Stage)

• Extracorporeal photopheresis — blood is drawn, treated with light, and returned
• Targeted therapies like brentuximab vedotin (CD30-positive disease) and mogamulizumab
• Systemic chemotherapy
• Allogeneic stem cell transplantation in select advanced cases

For many patients, the goal isn’t curing CTCL — it’s keeping it in long-term remission so they can live a normal life. And for the most common form, mycosis fungoides, that’s often achievable.

Prognosis: What Patients Want to Know

Survival depends heavily on type and stage:

• Early-stage mycosis fungoides has a near-normal life expectancy. Many patients live for decades after diagnosis.
• Advanced mycosis fungoides with tumor or organ involvement has a more guarded prognosis.
• Sézary syndrome is more aggressive, with median survival historically around 3 years, though newer therapies have improved outcomes.

Early diagnosis is the single biggest factor in long-term outcome — which is precisely why anything that delays diagnosis is so dangerous.

CTCL and the Dupixent Question

Over the past few years, dermatology journals have published a growing number of case reports and observational studies suggesting that patients on the eczema biologic Dupixent (dupilumab) are being diagnosed with CTCL at higher rates than would be expected. A 2024 study in Dermatologic Therapy found Dupixent users were roughly 4.6 times more likely to be diagnosed with CTCL than non-users. A 2025 analysis of FDA adverse event data found CTCL was reported about 30 times more often in Dupixent users than in users of other medications.

In March 2025, the FDA added Dupixent to its Potential Signals of Serious Risk list, citing CTCL as the safety concern under review.

The leading hypotheses are that Dupixent’s powerful suppression of inflammation may be:

• Masking an early CTCL that was already there, allowing it to progress silently
• Accelerating the progression of CTCL through its effects on the IL-4 and IL-13 immune signaling pathways
• A combination of both

If you’ve been diagnosed with CTCL after taking Dupixent, our Dupixent lawsuit page explains your legal options and our analysis of whether Dupixent can cause cancer goes deeper into the science and the litigation.

Reliable Patient Resources

If you or someone you love has been diagnosed with CTCL, these are reputable starting points:

• The American Academy of Dermatology’s CTCL overview
• The Cleveland Clinic’s cutaneous T-cell lymphoma guide
• Penn Medicine’s CTCL specialist program

Patients with CTCL — particularly Sézary syndrome — generally do best with care at a center that has a dedicated cutaneous lymphoma team.

When to Talk to a Lawyer

If your CTCL diagnosis came after a period of treatment with Dupixent, you may have a legal claim. The Tennessee statute of limitations for personal injury is generally one year under Tenn. Code § 28-3-104, and although discovery rules can extend it in some drug-injury cases, you should not wait to find out.

The Higgins Firm offers free, confidential case reviews for patients diagnosed with CTCL, mycosis fungoides, or Sézary syndrome after Dupixent use. We work on a contingency fee — you don’t pay unless we recover compensation for you.