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patients in the community at large, it is present in 70% of PTLDs. Surprisingly, one of the most common extranodal sites is the central nervous system, which is involved in 21% of cases. Another remarkable finding is the frequency of either macroscopic or microscopic allograft involvement, which occurs in 23% of patients with PTLD. In some patients the infiltrate is mistaken for rejection when allograft biopsies are studied microscopically. It is disappointing that 16% of patients with PTLD die without treatment, either because the diagnosis is missed, or is made too late to save them. Following treatment complete remissions are obtained in 38% of patients.

Kaposi's sarcoma (KS) is most common in transplant patients who are Arab, black, Italian, Jewish, Turkish or Greek.1-3 It occurred in 1.6% of 820 Italian renal transplant recipients,10 but was the most common neoplasm in renal transplant recipients in Saudi Arabia, comprising 76% of all malignancies.11

A clinician should suspect KS whenever a transplant patient, particularly one belonging to the ethnic groups described above, presents with reddish blue macules or plaques in the skin or oropharyngeal mucosa, or apparently infected granulomas that fail to heal.3,4 If the diagnosis is confirmed, a thorough workup including CT scans of the chest and abdomen and upper and lower gastrointestinal endoscopy, is necessary to exclude any internal visceral involvement.

Nonvisceral KS occurs in 59% of patients and is confined to the skin, or oropharyngeal mucosa and 41 % have visceral disease, involving mainly the gastrointestinal tract, lungs, and lymph nodes, but other organs are also affected.3,4 In patients with nonvisceral disease the lesions are confined to the skin in 98% and the mouth or oropharynx in 2%. Patients with visceral lesions have no skin involvement in 27%, but 3% have oral involvement which provides an accessible site for biopsy and diagnosis. The outlook of patients with nonvisceral disease is much more favorable than those with visceral disease, as 54% of the former group have complete remissions following treatment compared with only 30% in the latter.3,4

Most renal carcinomas in renal recipients arise in their own diseased kidneys although 10% occur in the allografts.3,4 Unlike most other neoplasms, that arise as complications of immunosuppressive therapy, many renal carcinomas are related to the underlying kidney disease necessitating transplantation. One contributary factor is analgesic nephropathy in renal allograft recipients, which occurs in 8% of CTTR patients with carcinomas of their native kidneys. This disorder is known to cause carcinomas in various parts of the urinary tract. This is borne out in the CTTR series in which 59% of patients with analgesia-related renal carcinomas have similar neoplasms elsewhere in the urinary tract.3,4 Another predisposing cause of cancers is acquired cystic disease of the native kidneys, which, in dialysis patients, is complicated by an increased incidence of renal carcinomas. The exact incidence of such carcinomas in renal transplant recipients is not known, but at least 17 patients in the CTTR have this disorder.3,4

A group of carcinomas arise in the vulva in females, the penis or scrotum in males, and in the perineum, perianal skin or anus in either sex.3,4 Sometimes female patients have multifocal lesions that involve not only of the vulva and perineum but also the vagina and/or uterine cervix. Females outnumber males by 2.6:1 in

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