What type of cancer has an increased incidence in transplant recipients?

Increased Cancer Risk in Transplant Recipients

Transplant recipients have a significantly increased risk of anal cancer compared to the general population, with a standardized incidence ratio (SIR) of approximately 6.8-fold higher than the general population. 1

HPV-Related Cancers in Transplant Recipients

• Anal cancer is strongly associated with human papillomavirus (HPV) infection, which is present in 80-85% of anal cancers, and immune suppression in transplant recipients significantly increases the risk of persistent HPV infection and subsequent malignancy 2, 3
• Solid organ transplant (SOT) recipients have approximately 2-4 fold increased incidence rate of all types of cancer, and a 3-5 fold increased rate of cancer mortality compared to the general population 2
• Among gynecologic and anogenital cancers in transplant recipients, HPV-related cancers show consistently and strongly elevated standardized incidence ratios (SIRs) 2

Specific Cancer Types with Increased Risk

• Vulvar and vaginal cancers show the highest risk elevation in transplant recipients with SIRs ranging from 7.3 to 23.9 2
• Anal squamous cell carcinoma shows a pooled SIR of 6.8 (95% CI, 4.3-10.9) with an absolute incidence rate of 12.3 per 100,000 person-years in transplant recipients 1
• Cervical cancer risk is moderately increased in transplant recipients with SIRs ranging from 2.0 to 5.7 across studies 2
• Female kidney transplant recipients have significantly higher prevalence of cervical high-risk HPV (35.5%) compared to immunocompetent controls (18.2%) 4

Risk Factors and Mechanisms

• Immunosuppressive therapy required to prevent graft rejection increases the risk of HPV persistence and malignant transformation 2, 3
• The average time from transplant to diagnosis of anal disease is 11.67 years, with odds of anal disease increasing by 4% each year post-transplant 5
• Female sex (OR 1.96) and history of genitourinary HPV disease (OR 69.63) are significant risk predictors for anal disease in transplant recipients 5
• Prevalence of anal high-risk HPV is significantly higher in female kidney transplant recipients (45.5%) compared to immunocompetent controls (27.2%) 6

Screening and Prevention

• HPV vaccination is recommended for transplant recipients, particularly before transplantation and immunosuppressive therapy to ensure high immunogenicity 2
• The quadrivalent or nonavalent HPV vaccines are preferred given the high prevalence of anogenital warts in immunosuppressed patients 2
• Closer surveillance for cervical cancers is warranted in transplant recipients due to the increased risk 2
• Anal screenings should be targeted to higher-risk subsets: female recipients farther out from transplant and patients with genitourinary HPV-related diseases 5

Clinical Implications

• Co-infection with anal and cervical high-risk HPV is common in female kidney transplant recipients (27.3% vs 6.6% in controls) 4
• Prevalence of abnormal anal cytology in transplant recipients is approximately 12.9%, with 4.7% showing high-grade squamous intraepithelial lesions 1
• Most early-stage anal cancers are asymptomatic due to their typically slow growth pattern, which can lead to delayed diagnosis 3, 7
• Immunosuppression can accelerate the progression of precancerous lesions to invasive cancer 7

Based on the evidence presented, anal cancer shows the most consistently elevated risk among transplant recipients compared to the general population, with a standardized incidence ratio of approximately 6.8. Therefore, the correct answer is (b) anal cancer.