A 9-year-old girl presents with a unilateral breast lump. What is the most appropriate next step in the management?

In the case of a 9-year-old girl presenting with a unilateral breast lump, the most appropriate next step in management is reassurance and anticipatory guidance. This approach is suitable because breast development can occur at varying ages, and finding a breast lump in a young girl is not uncommon. Many cases are simply related to normal physiological changes during puberty.

At this age, most breast changes are typically benign, such as juvenile breast tissue hyperplasia or normal physiological developmental changes. Providing reassurance and guidance helps to address parental concerns while also educating about typical developmental milestones. Educating the family about what to expect during puberty can be very beneficial, particularly in what signs and symptoms to monitor for in the future.

The other options would not be appropriate first steps. For example, transdermal ethinyl estradiol would be inappropriate as it is a hormonal treatment that is not indicated for a simple breast lump in an otherwise healthy prepubertal girl. Measuring serum LH is more relevant in cases where precocious puberty is suspected, but given the context of a unilateral lump, it is not the immediate concern. Mammography, while useful for evaluating suspicious breast lumps, is generally reserved for older adolescents/adults and is not typically performed in prepubescent children unless there