post transplant lymphoproliferative disorder

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Post-transplant lymphoproliferative disorder (PTLD), also referred as post-transplant lymphoproliferation disorder, represents a variety of conditions ranging from lymphoid hyperplasia to malignancy, included in the WHO classification of tumors of hematopoietic and lymphoid tissues. It can be a life-threatening fulminant disorder.

Epidemiology

PTLD develops in no more than 2% of all patients who receive transplants, somewhat higher in pediatric patients . It is the second most common type of malignancy in post-transplant patients with two peaks demonstrated - at one-year post-transplant and at 4-5 years post-transplant . The incidence varies according to the type of transplant :

small bowel: high
pancreas: 12%
heart and lung: 3-9%
liver: 1-2%
cardiac: 1-2%
renal: 1-2%
hematopoietic stem cell transplant: 0.6-1.2%

Risk factors

Some risk factors are recognized, including :

Epstein-Barr virus seronegativity at the time of transplantation (which may explain why the incidence of PTLD is higher in children)
concomitant cytomegalovirus infection
allograft type

The immunosuppressive regime also affects the distribution of PTLD:

azathioprine: more common CNS and allograft involvement
cyclosporine or FK-506: gastrointestinal tract and lymph nodes

Clinical presentation

Clinical presentation is variable, both in symptomatology and severity, ranging from flu-like symptoms with fever and malaise to fulminant systemic disease . It of course also varies with the location of the PTLD (see below).

The time between transplant and development of PTLD is also variable, ranging from 1 month to 7 years , with most occurring within a year . As a general rule, patients who present late (>1 year) have more aggressive tumors with poorer prognosis .

Pathology

Most PTLD specimens demonstrate a polyclonal B-cell Epstein-Barr virus (EBV) positive cell population . Monoclonal B-cell and T-cell small bowel lymphomas do occur in patients with organ transplants but are less frequent.

When PTLD develops in hematopoietic stem cell transplant recipients, it usually arises from the donor cells .

Macroscopic appearance

Macroscopically these tumors have been likened to uncooked fish flesh.

Histology

These tumors range from low-grade/benign lymphoid hyperplasia to high-grade malignant non-Hodgkin lymphoma.

Location

PTLD may be focal or diffuse and can affect almost any organ system and even the allograft. It usually manifests as an extranodal disease, and it can occur in a variety of locations, including :

abdominal
- liver: most common
- small bowel
- colon and stomach less common
chest
- lung
head and neck
primary central nervous system PTLD
osseous: rare
cutaneous

Radiographic features

The range of appearances is large due to the number of possible sites. In general extranodal involvement is 3-4 times more common than nodal involvement, and resembles primary lymphoma of those organs :

solid organs (liver, spleen, kidney)
- nodules
  - hypoechoic
  - low density on CT
- diffuse infiltration
bowel
- circumferential wall thickening
- aneurysmal dilatation
- ulceration/perforation
- bowel obstruction uncommon
lung/pleura
- nodules
  - usually homogeneous
  - may centrally cavitate
- diffuse infiltration
brain
- similar to lymphoma in the setting of HIV infection
- necrosis and hemorrhage more common than in run-of-the-mill primary CNS lymphoma
nodes
- non-specific nodal enlargement, similar to other lymphomas
- most commonly affecting mediastinum (either lymphadenopathy or anterior mediastinal mass) or retroperitoneum (either as lymphadenopathy or mass)

Treatment and prognosis

Treatment is variable and depends on the location and extent of disease. Options include :

reduction of immunosuppression
surgical resection of localized disease
radiotherapy
medical agents
- alpha interferon therapy
- antiviral therapy (limited success)
- IL-2 infusions
- rituximab

Prognosis depends on the grade of the lymphoma, and cell type: the low-grade lymphoid proliferation of polyclonal B-cell origin with EBV implication have a better prognosis than other cell types of higher grade. Five-year survival is ~35% .

Disease regression in response to a reduction in immunosuppression is a unique diagnostic feature of PTLD and distinguishes this condition from other malignant diseases. Patients should be closely monitored for allograft rejection.