The development of bleomycin-associated pulmonary fibrosis with permanent restrictive disease is dose dependent, usually occurring at doses greater than 200 U/m2 to 400 U/m2, higher than those used in treatment protocols for pediatric malignancies.[5,6,7] More current pediatric regimens for Hodgkin lymphoma using radiation therapy and ABVD (doxorubicin, bleomycin, vinblastine, and dacarbazine) have shown a significant incidence of asymptomatic pulmonary dysfunction after treatment, which appears to improve with time.[8,9,10] However, grade 3 and 4 pulmonary toxicity has been reported in 9% of children receiving 12 cycles of ABVD followed by 21 Gy of radiation. In addition, ABVD-related pulmonary toxicity may result from fibrosis induced by bleomycin or "radiation recall" pneumonitis related to administration of doxorubicin. Pulmonary veno-occlusive disease has been observed rarely and has been attributed to bleomycin chemotherapy.
Patients undergoing hematopoietic stem cell transplant (HSCT) are at increased risk of pulmonary toxicity, related to (1) preexisting pulmonary dysfunction (e.g., asthma, pretransplant therapy); (2) the preparative regimen that may include cyclophosphamide, busulfan, and carmustine; (3) total-body irradiation; and (4) the presence of GVHD.[12,13,14,15,16,17] Although most survivors of transplant are not clinically compromised, restrictive lung disease may occur and has been reported to increase in prevalence with increasing time from HSCT, based on limited data from longitudinally followed cohorts.[18,19] Obstructive disease is less common, as is late onset pulmonary syndrome, which includes the spectrum of restrictive and obstructive disease. Bronchiolitis obliterans with or without organizing pneumonia, diffuse alveolar damage, and interstitial pneumonia may occur as a component of this syndrome, generally between 6 and 12 months posttransplant. Cough, dyspnea, or wheezing may occur with either normal chest x-ray or diffuse/patchy infiltrates; however, most patients are symptom free.[14,20,21,22]
Additional factors contributing to chronic pulmonary toxicity include superimposed infection, underlying pneumonopathy (e.g., asthma), cigarette use, respiratory toxicity, chronic GVHD, and the effects of chronic pulmonary involvement by tumor or reaction to tumor. Lung lobectomy during childhood appears to have no significant impact on long-term pulmonary function, but the long-term effect of lung surgery for children with cancer is not well defined.
The true prevalence or incidence of pulmonary dysfunction in childhood cancer survivors is not clear. For children treated with HSCT, there is significant clinical disease. No large cohort studies have been performed with clinical evaluations coupled with functional and quality of life assessments. An analysis of self-reported pulmonary complications of 12,390 survivors of common childhood malignancies has been reported by the Childhood Cancer Survivor Study. This cohort includes children treated with both conventional and myeloablative therapies. Compared with siblings, survivors had an increased relative risk (RR) of lung fibrosis, recurrent pneumonia, chronic cough, pleurisy, use of supplemental oxygen therapy, abnormal chest wall, exercise-induced shortness of breath, and bronchitis, with RRs ranging from 1.2 to 13.0 (highest for lung fibrosis and lowest for bronchitis). The 25-year cumulative incidence of lung fibrosis was 5% for those who received chest radiation therapy and less than 1% for those who received pulmonary toxic chemotherapy. With changes in the doses of radiation therapy employed since the late 1980s, the incidence of these abnormalities is likely to decrease.