Objective: To demonstrate that expectant observation of young infants with small adrenal masses would result in excellent event-free and overall survival.

Background: Neuroblastoma is the most common malignant tumor in infants, and in young infants, 90% of neuroblastomas are located in the adrenal gland. Although surgical resection is standard therapy, multiple observations suggest that expectant observation could be a safe alternative for infants younger than 6 months who have small adrenal masses.

Methods: A prospective study of infants younger than 6 months with small adrenal masses and no evidence of spreading beyond the primary tumor was performed at participating Children's Oncology Group institutions. Parents could choose observation or immediate surgical resection. Serial abdominal sonograms and urinary vanillylmandelic acid and homovanillic acid measurements were performed during a 90-week interval. Infants experiencing a 50% increase in the volume of the mass, urine catecholamine values, or an increase in the homovanillic acid to vanillylmandelic acid ratio greater than 2, were referred for surgical resection.

Results: Eighty-seven eligible patients were enrolled: 83 elected observation and 4 chose immediate surgery. Sixteen observational patients ultimately had surgery; 8 had International Neuroblastoma Staging System stage 1 neuroblastoma, 2 had higher staged neuroblastoma (2B and 4S), 2 had low-grade adrenocortical neoplasm, 2 had adrenal hemorrhage, and 2 had extralobar pulmonary sequestration. The 2 patients with adrenocortical tumors were resected because of a more than 50% increase in tumor volume. The 3-year event-free survival for a neuroblastoma event was 97.7 ± 2.2% within the entire cohort of patients (n = 87). The 3-year overall survival was 100%, with a median follow-up of 3.2 years. Eighty-one percent of patients on the observation arm were spared resection.

Conclusions: Expectant observation of infants younger than 6 months with small adrenal masses led to excellent event-free survival and overall survival while avoiding surgical intervention in a large majority of the patients.