In a patient with anaplastic large‑cell lymphoma lacking cutaneous involvement, what are the differential diagnoses, recommended work‑up, and appropriate first‑line therapy?

Systemic Anaplastic Large-Cell Lymphoma Without Cutaneous Involvement

In a patient with anaplastic large-cell lymphoma lacking cutaneous involvement, you are dealing with systemic ALCL, which requires immediate distinction between ALK-positive and ALK-negative disease through immunohistochemistry, as this fundamentally determines prognosis and treatment approach—ALK-positive disease warrants anthracycline-based chemotherapy (CHOP or CHOEP) with expected 5-year survival of 70-90%, while ALK-negative disease has significantly worse outcomes (40-60% 5-year survival) and may require more aggressive strategies.

Critical Differential Diagnoses

The absence of cutaneous involvement immediately excludes primary cutaneous ALCL (which by definition requires skin-only disease) and points toward systemic ALCL 1. However, the broad differential includes:

• Other aggressive lymphomas: Diffuse large B-cell lymphoma, peripheral T-cell lymphoma NOS, classical Hodgkin lymphoma 2
• Solid malignancies: Carcinoma and melanoma (due to anaplastic morphology) 2
• Myeloid neoplasms: Myeloid sarcoma 2
• Transformed mycosis fungoides: If patches/plaques preceded nodal disease 1

Key diagnostic pitfall: The anaplastic morphology can mimic carcinoma, and some cases aberrantly express cytokeratin or CD15, potentially leading to misdiagnosis 2. Always confirm CD30 expression in ≥75% of tumor cells and perform comprehensive T-cell marker panels.

Essential Work-Up

Histopathologic Confirmation

• Tissue biopsy showing large pleomorphic/anaplastic cells with hallmark morphology (eccentric horseshoe-shaped nuclei) 3
• Immunophenotype: CD30+ (≥75% of cells), typically CD4+, variable loss of pan-T-cell antigens (CD2, CD3, CD5) 1
• ALK status by immunohistochemistry: This is the single most critical prognostic marker 4, 3
  • If ALK-positive: Look for NPM-ALK t(2;5) translocation
  • If ALK-negative: Consider testing for DUSP22 or TP63 rearrangements (emerging prognostic markers) 4

Staging Investigations

• Complete history: B-symptoms (fever, night sweats, weight loss), prior lymphoid malignancies (especially Hodgkin lymphoma), immunosuppression status 1
• Physical examination: Lymphadenopathy (nodes >1.5 cm require biopsy), hepatosplenomegaly 1
• Laboratory: CBC with differential, comprehensive metabolic panel, LDH 1
• Imaging: Contrast-enhanced CT chest/abdomen/pelvis with or without PET/CT 1
• Bone marrow biopsy: Recommended for complete staging 1

Critical distinction: Unlike primary cutaneous ALCL where extensive staging may be unnecessary, systemic ALCL requires full staging workup given frequent extranodal involvement (40% present with advanced stage) 3.

First-Line Therapy

ALK-Positive ALCL

Standard treatment is anthracycline-based polychemotherapy 4, 3:

• CHOP (cyclophosphamide, doxorubicin, vincristine, prednisone) achieves ~90% overall response rate 3
• CHOEP (CHOP plus etoposide) is an alternative with similar efficacy 5, 3
• Expected outcomes: 5-year relapse-free survival ~60%, 5-year overall survival ~70% 3

Young age is a strong favorable prognostic factor beyond ALK status alone 4. The International Prognostic Index (IPI) effectively risk-stratifies these patients 3.

ALK-Negative ALCL

More aggressive disease requiring anthracycline-based chemotherapy, but outcomes are inferior 4:

• First-line CHOP remains standard, but many patients fail 4
• Consider consolidative autologous stem cell transplantation in first remission for appropriate candidates, though superiority over chemotherapy alone is unproven 4, 3
• Genetic heterogeneity (DUSP22 vs TP63 rearrangements) may guide future risk-adapted approaches 4

Emerging Targeted Therapies

• Brentuximab vedotin (anti-CD30 antibody-drug conjugate): 86% response rate in relapsed/refractory disease, under investigation for first-line use 5, 4, 6
• ALK inhibitors (crizotinib, alectinib, ceritinib): Relevant for ALK-positive disease, particularly in relapsed settings 5

Key Clinical Pitfalls

1. Do not confuse with primary cutaneous ALCL: Systemic disease has dramatically worse prognosis and requires aggressive chemotherapy, not conservative skin-directed therapy 6, 7

2. ALK testing is mandatory: This single marker divides the disease into two prognostically distinct entities 4, 3

3. Beware of diagnostic mimics: Anaplastic morphology, potential cytokeratin expression, and CD15 positivity can lead to misdiagnosis as carcinoma or Hodgkin lymphoma 2

4. Age matters independently: Young patients with ALK-positive disease have particularly favorable outcomes 4

5. Upfront transplant role unclear: While autologous transplant salvages relapsed disease effectively, its benefit in first remission remains investigational for ALK-positive disease 3