ALK-positive Anaplastic Large Cell Lymphoma (ALK+ ALCL)

ALK-positive anaplastic large cell lymphoma (ALK+ ALCL) is an aggressive lymphoma arising from mature T cells. It is a subtype of systemic anaplastic large cell lymphoma.

The lymphoma cells typically express CD30 and ALK protein. Most cases harbor an ALK gene rearrangement, most commonly the NPM1::ALK fusion. This genetic alteration leads to persistent activation of ALK signaling, promoting the growth and survival of lymphoma cells.

ALK+ ALCL can occur at any age but is more common in children, adolescents, and young adults. Patients may present with involvement of multiple lymph node regions. Extranodal disease may affect the skin, bones, lungs, liver, or other tissues.

Although ALK+ ALCL generally has a more favorable prognosis than ALK-negative ALCL, it remains an aggressive disease, and some patients may experience relapse or refractory disease.

The exact cause of ALK+ ALCL is not fully understood.

The defining molecular feature is an ALK gene rearrangement. ALK may fuse with other genes, most commonly NPM1, producing an abnormally active fusion protein. This activates intracellular signaling pathways that promote the proliferation and survival of malignant T cells.

ALK rearrangements are generally acquired genetic changes in tumor cells rather than inherited mutations passed from parents to children.

No specific lifestyle, dietary, or environmental factor has been clearly established as a direct cause of ALK+ ALCL. Most patients have no identifiable cause.

ALK+ ALCL often progresses rapidly. Symptoms depend on the location and extent of lymphoma involvement.

Possible signs and symptoms include:

• Painless enlargement of lymph nodes in the neck, armpits, or groin

• Persistent or recurrent unexplained fever

• Drenching night sweats

• Unintentional weight loss

• Fatigue or general weakness

• Skin nodules, masses, or other abnormal lesions

• Localized pain when bones are involved

• Cough, chest discomfort, or difficulty breathing with chest or lung involvement

• Abdominal pain or swelling when abdominal lymph nodes or organs are affected

Some patients have extensive nodal or extranodal involvement at diagnosis.

These symptoms are not specific to ALK+ ALCL and may also occur with infections or inflammatory conditions. Further evaluation is needed to establish the diagnosis.

Diagnosis of ALK+ ALCL requires a combination of clinical findings, tissue pathology, immunohistochemistry, and, when necessary, molecular genetic testing.

A biopsy of affected tissue is usually required to confirm the diagnosis. Blood tests, imaging, and other assessments may be performed to determine the extent and stage of the disease.

Tissue Biopsy and Pathology

Tissue biopsy is one of the most important tests for diagnosing ALK+ ALCL.

A lymph node excision or biopsy of another affected tissue is usually performed. Pathological examination may reveal large, atypical lymphoma cells, some with characteristic horseshoe-shaped or kidney-shaped nuclei.

The diagnosis is based on a combination of cell morphology, tissue architecture, and immunophenotypic findings.

Immunohistochemistry

Immunohistochemistry is essential for confirming ALK+ ALCL and distinguishing it from other lymphomas.

Typical findings include:

• Strong, usually diffuse CD30 expression

• Positive ALK protein expression

• Variable or absent expression of some T-cell-associated markers

• Variable expression of other immunophenotypic markers

CD30 and ALK are important diagnostic markers, but the final diagnosis requires correlation with morphology and other findings.

ALK Genetic Testing

ALK+ ALCL is typically associated with ALK gene rearrangements, most commonly the NPM1::ALK fusion.

In selected cases, fluorescence in situ hybridization (FISH) or other molecular tests may be used to confirm ALK rearrangements and identify fusion partners.

These tests help characterize the molecular features of the disease, although comprehensive fusion testing is not required in every case.

Blood Tests

Blood tests usually include a complete blood count, liver and kidney function tests, and lactate dehydrogenase (LDH).

These tests help assess overall health, organ function, and certain markers associated with disease activity.

Elevated LDH may be associated with tumor burden or tissue damage, but it cannot independently establish the diagnosis of ALK+ ALCL.

Imaging Tests

Imaging is usually performed after diagnosis to assess the extent of ALK+ ALCL.

Commonly used imaging tests include PET/CT and CT. PET/CT can help identify nodal and extranodal disease and assess treatment response in selected patients.

The choice of imaging depends on age, clinical presentation, and the treatment plan.

Bone Marrow Tests

Bone marrow involvement may occur in ALK+ ALCL, but bone marrow aspiration or biopsy is not routinely required for every patient.

Bone marrow evaluation may be considered when blood tests are abnormal, imaging suggests marrow involvement, or other clinical findings raise suspicion.

ALK+ ALCL is an aggressive lymphoma that usually requires systemic treatment.

Treatment depends on age, disease stage, tumor burden, previous therapies, treatment response, and overall health.

Initial treatment generally involves multi-agent chemotherapy. CD30-targeted antibody-drug conjugates, ALK inhibitors, or other therapies may be used in selected patients.

For relapsed or refractory disease, treatment decisions require reassessment of disease status and previous treatment responses.

Combination Chemotherapy

Multi-agent chemotherapy is a major treatment approach for ALK+ ALCL.

Adults may receive CHOP-based or other chemotherapy regimens. Brentuximab vedotin-containing combinations may be used in eligible patients.

Children and adolescents are generally treated with age-appropriate multi-agent chemotherapy protocols, which differ from adult treatment strategies.

Treatment response and potential adverse effects, including infections and myelosuppression, require regular monitoring.

CD30-Targeted Therapy

ALK+ ALCL cells typically express CD30, making it an important therapeutic target.

Brentuximab vedotin (BV) is a CD30-directed antibody-drug conjugate that delivers a cytotoxic agent to CD30-expressing tumor cells.

It may be combined with chemotherapy in selected patients or used for relapsed or refractory disease, depending on approved indications and previous treatment.

Its use depends on age, disease status, drug availability, and local regulatory approvals.

ALK Inhibitor Therapy

ALK rearrangements are a defining molecular feature of ALK+ ALCL and provide a rationale for targeted therapy.

ALK inhibitors block the abnormal kinase activity of ALK fusion proteins, disrupting signaling pathways involved in lymphoma cell growth and survival.

ALK inhibitors such as crizotinib have demonstrated antitumor activity in selected patients with relapsed or refractory ALK+ ALCL.

Their use depends on age, previous treatments, disease status, and local regulatory approvals. Not every patient with ALK+ ALCL requires an ALK inhibitor.

Radiation Therapy

Radiation therapy is not routinely required for all patients with ALK+ ALCL.

It may be considered in selected patients with localized disease, residual lesions, or symptoms caused by specific tumor sites.

The decision depends on disease location, extent, previous treatment, and potential adverse effects.

Hematopoietic Stem Cell Transplantation (HSCT)

Hematopoietic stem cell transplantation (HSCT) is not routinely recommended for all patients with ALK+ ALCL, particularly those who respond well to initial treatment.

For selected patients with relapsed or refractory disease, autologous or allogeneic HSCT may be considered after achieving disease control.

The decision depends on age, overall health, relapse characteristics, treatment response, donor availability, and other treatment options.

Treatment of Relapsed or Refractory Disease

Some patients with ALK+ ALCL may relapse after initial treatment or fail to achieve adequate disease control.

For relapsed or refractory disease, reassessment of disease extent, pathology, previous therapies, and overall health is important.

Treatment options may include salvage chemotherapy, CD30-targeted therapy, ALK inhibitors, or hematopoietic stem cell transplantation.

Because relapse patterns and treatment responses vary, management should be individualized.

Clinical Trials

Treatment for ALK+ ALCL continues to evolve. Clinical trials are investigating newer ALK inhibitors, immunotherapies, and combinations of different treatments.

Patients with relapsed or refractory disease, particularly those with limited standard treatment options, may discuss participation in suitable clinical trials with their healthcare team.