Adult T-Cell Leukemia/Lymphoma

• HTLV-1 is a retrovirus that infects CD4-positive T cells and, unlike HIV, causes clonal proliferation rather than cell death. It spreads primarily by cell-to-cell contact, which is why cell-free blood products and breast milk differ so much in infectivity
• The viral Tax protein is the principal early driver: it activates NF-κB, CREB and AP-1, drives IL-2 and IL-2 receptor (CD25) expression creating an autocrine growth loop, and inactivates p53 and cell-cycle checkpoints while impairing DNA repair — producing genomic instability
• Tax is highly immunogenic, so established tumours frequently silence Tax expression to escape cytotoxic T-cell surveillance. The viral protein HBZ, encoded on the antisense strand, is expressed persistently in all cases and sustains proliferation once Tax is switched off
• Accumulated somatic mutations — commonly in CCR4, PLCG1, PRKCB, STAT3, TP53 and CD28 — complete transformation. The long latency reflects the time required to accumulate them
• CCR4 is expressed on most ATLL cells, driving skin homing (hence frequent cutaneous involvement) and providing the target for mogamulizumab
• Hypercalcaemia arises chiefly from tumour-derived PTHrP, with contributions from RANK ligand and inflammatory cytokines, producing widespread osteoclastic bone resorption — typically without discrete lytic metastatic deposits
• Immunosuppression results from loss of normal T-cell function, compounded by the fact that many ATLL cells have a regulatory T-cell-like (FoxP3-positive) phenotype that actively suppresses immunity

• HTLV-1 infection is necessary — no case occurs without it
• Endemic regions: southwestern Japan (Kyushu, Okinawa), the Caribbean, West and Central Africa, South America (notably Peru, Brazil, Colombia), Iran (Mashhad), and Melanesia. In non-endemic countries the disease occurs in migrants from these areas — a migration history is essential
• Transmission routes:
• Breastfeeding — the dominant route and the one that matters for disease risk. Prolonged breastfeeding beyond six months substantially increases the likelihood of infection
• Sexual transmission, more efficient male-to-female
• Blood transfusion of cellular components (not plasma or fractionated products) and injection drug use
• Infection in infancy is the key determinant of ATLL risk. Those infected as adults rarely develop ATLL, though they may develop HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP)
• Latency of 20-60 years; median age at diagnosis around 60 overall, but considerably younger in Caribbean and South American populations
• High proviral load and the presence of an expanded clone predict progression
• Lifetime risk among the infected is only 3-5%, and higher in men

The four subtypes — the framework that determines everything

• Acute type (~55-60%): the classic aggressive presentation — leukaemic phase with markedly elevated white count, hypercalcaemia, elevated LDH, generalized lymphadenopathy, hepatosplenomegaly, skin lesions and rapid deterioration. Survival measured in months without treatment
• Lymphomatous type (~20%): prominent lymphadenopathy without a leukaemic phase; hypercalcaemia common; similarly aggressive
• Chronic type (~15%): lymphocytosis with mild skin and nodal involvement, normal calcium, more indolent — but subdivided into favourable and unfavourable variants by LDH, albumin and urea, with the unfavourable group behaving aggressively
• Smouldering type (~5%): skin or pulmonary lesions with under 5% circulating abnormal cells, normal calcium, indolent, often stable for years — but with continuing risk of acute transformation

Clinical features

• Hypercalcaemia in the majority of acute-type patients: polyuria, thirst, constipation, nausea, confusion, lethargy, and acute kidney injury. It may be the presenting problem, with the lymphoma found during its work-up
• Skin involvement in around half — papules, nodules, plaques, erythroderma or tumours, closely mimicking mycosis fungoides
• Generalized lymphadenopathy and hepatosplenomegaly
• Lytic bone lesions and pathological fracture, though hypercalcaemia often occurs without them
• Opportunistic infection reflecting profound cellular immunodeficiency: Pneumocystis jirovecii pneumonia, cytomegalovirus, disseminated fungal infection, cryptococcosis, and herpes zoster, often multidermatomal
• ***Strongyloides stercoralis* hyperinfection and disseminated strongyloidiasis — larvae disseminate with Gram-negative bacteraemia and meningitis. Corticosteroid administration is the classic precipitant**, which makes this a treatment-induced catastrophe in an untested patient
• CNS involvement in a minority, with leptomeningeal disease
• Markedly elevated LDH; eosinophilia is common
• Note that HTLV-1 also causes HAM/TSP — a slowly progressive spastic paraparesis with bladder dysfunction — and infective dermatitis and uveitis; these are separate manifestations of the same infection, not part of ATLL

• HTLV-1 serology by ELISA with Western blot or PCR confirmation — required in every suspected case. Ask about country of birth, maternal origin and breastfeeding history
• Peripheral blood film: the characteristic "flower cells" (also called cloverleaf cells) — mature lymphocytes with markedly polylobated, convoluted nuclei and condensed chromatin. Highly characteristic, though not present in the lymphomatous type
• Immunophenotype: CD2, CD3, CD4, CD5 positive; CD7 negative (a loss shared with mycosis fungoides); CD8 negative; and CD25 (IL-2 receptor alpha) strongly positive — a useful discriminator. Many cases are FoxP3-positive, reflecting a regulatory T-cell-like phenotype. CCR4 positive in the majority
• Demonstration of clonally integrated HTLV-1 provirus in the tumour cells by Southern blot or PCR distinguishes ATLL from an incidental HTLV-1 infection in a patient with a different T-cell lymphoma — an important distinction in endemic areas
• Lymph node or skin biopsy where there is no leukaemic phase
• Calcium, LDH, albumin, urea and creatinine — used for both subtype classification and prognosis
• ***Strongyloides* screening in every patient — serology plus stool examination — before corticosteroids are given**. Empirical ivermectin is reasonable in patients from endemic areas when results will be delayed
• Staging: CT or PET-CT, bone marrow examination, and lumbar puncture where neurological features exist
• Baseline hepatitis B and C, HIV, and CMV serology

Differential diagnosis

• Mycosis fungoides and Sézary syndrome — the closest mimic; separated by HTLV-1 serology, CD25 positivity, hypercalcaemia and flower cells
• Peripheral T-cell lymphoma, not otherwise specified, in an HTLV-1-negative patient
• Other causes of malignancy-associated hypercalcaemia
• T-prolymphocytic leukaemia and Sézary syndrome in the leukaemic differential

Treat the hypercalcaemia and screen for Strongyloides first

• Aggressive intravenous saline rehydration, followed by bisphosphonates (zoledronic acid) or denosumab where renal function precludes bisphosphonates. Calcitonin provides rapid but transient control. Avoid thiazides and volume depletion
• ***Strongyloides* screening and empirical ivermectin before corticosteroids*** — this single step prevents a fatal hyperinfection syndrome
• Tumour lysis prophylaxis with hydration and allopurinol or rasburicase in high-burden disease

By subtype

• Smouldering and favourable chronic types: watchful waiting with skin-directed therapy for cutaneous lesions. Intensive treatment has not shown benefit, though the emerging alternative of antiviral therapy is discussed below
• Acute, lymphomatous and unfavourable chronic types: systemic therapy, with the intent of proceeding to transplantation in suitable patients

Systemic options

• Intensive multi-agent chemotherapy — for example the dose-intensive LSG15/VCAP-AMP-VECP regimen used in Japan — produces higher response rates than CHOP but with substantial toxicity; responses are frequently short-lived
• Zidovudine with interferon-alfa is effective in the leukaemic (acute and chronic) subtypes, with meta-analytic data supporting improved survival, and is notably less effective in the lymphomatous type, where chemotherapy is preferred
• Mogamulizumab, an anti-CCR4 monoclonal antibody, is approved in Japan and active in relapsed and refractory disease. Note it increases the risk of severe graft-versus-host disease if allogeneic transplantation follows, so sequencing matters
• Allogeneic stem cell transplantation is the only curative modality, offering long-term survival to a minority, with graft-versus-ATLL effect contributing. It should be considered early in fit patients with aggressive subtypes, since remissions are short
• CNS prophylaxis with intrathecal chemotherapy in aggressive subtypes
• Antimicrobial prophylaxis against Pneumocystis, fungi and herpesviruses throughout treatment
• Clinical trial enrolment is appropriate at every stage given poor outcomes

Prevention — the most effective intervention available

• Avoidance of prolonged breastfeeding by HTLV-1-positive mothers dramatically reduces vertical transmission and, in Japan, antenatal screening with feeding counselling has produced a measurable fall in seroprevalence
• Screening of blood donors and leucodepletion of cellular products
• Barrier contraception and partner testing

Prognosis

• Acute type: median survival typically under a year; lymphomatous type similar
• Chronic type: several years, with the unfavourable variant behaving far worse
• Smouldering type: prolonged survival, with ongoing risk of acute transformation
• Adverse factors: hypercalcaemia, high LDH, poor performance status, age, and high numbers of involved sites

• Hypercalcaemia with acute kidney injury, arrhythmia, obtundation and coma — often the immediate threat to life at presentation
• ***Strongyloides* hyperinfection and dissemination**, frequently precipitated by corticosteroids, with polymicrobial Gram-negative bacteraemia and meningitis and a very high mortality
• Opportunistic infection: Pneumocystis pneumonia, cytomegalovirus, cryptococcosis, disseminated fungal disease, and disseminated or multidermatomal zoster
• Tumour lysis syndrome in high-burden acute disease
• Pathological fracture and bone pain from lytic lesions and osteoclastic resorption
• CNS involvement with leptomeningeal disease
• Acute transformation of smouldering or chronic disease into acute-type ATLL
• Treatment toxicity: profound myelosuppression and infection from intensive chemotherapy; mogamulizumab-associated severe graft-versus-host disease when allogeneic transplantation follows; transplant-related mortality
• Progressive refractory disease — the usual course in aggressive subtypes, with short remissions

• ATLL is caused by HTLV-1 — a retrovirus transmitted chiefly by breastfeeding, also sexually and by cellular blood products. Infection in infancy is what confers ATLL risk
• Latency is 20-60 years and lifetime risk among infected people is only 3-5% — a common infection causing an uncommon cancer, very slowly
• Hypercalcaemia is the signature — the most common cause of hypercalcaemia among lymphomas, driven by PTHrP and RANK ligand with osteoclast activation, and frequently occurring without discrete lytic lesions
• "Flower cells" (cloverleaf cells) — mature lymphocytes with markedly polylobated nuclei — on the blood film
• Immunophenotype: CD4-positive, CD25 strongly positive, CD7-negative, CD8-negative, often FoxP3-positive. CD25 helps separate it from mycosis fungoides
• **Screen for Strongyloides and give ivermectin before corticosteroids.** Steroid-precipitated hyperinfection with Gram-negative bacteraemia and meningitis is a classic, preventable, often fatal event
• Four subtypes govern management: acute and lymphomatous are aggressive and treated systemically; smouldering and favourable chronic are observed
• Zidovudine plus interferon-alfa works in the leukaemic subtypes (acute and chronic) and not in the lymphomatous type, where chemotherapy is preferred — an unusual instance of antiviral therapy treating a malignancy
• Allogeneic transplantation is the only curative option and should be considered early, because remissions are short
• Mogamulizumab targets CCR4 but increases severe graft-versus-host disease risk if transplantation follows — sequence carefully
• HTLV-1 also causes HAM/TSP (progressive spastic paraparesis with bladder dysfunction), uveitis and infective dermatitis — separate diseases from ATLL, same virus
• ATLL closely mimics mycosis fungoides on the skin — check HTLV-1 serology, calcium and CD25 before settling on a cutaneous T-cell lymphoma diagnosis, especially in patients from endemic regions
• Prevention beats treatment: avoiding prolonged breastfeeding by seropositive mothers has measurably reduced seroprevalence where it has been implemented