The father of a 1-week-old infant comes to the office in a panic. He has just noticed on his child a right anterior shoulder mass that seems tender. The father is an osteosarcoma survivor and fears the child has the same malignancy. In reviewing the baby's discharge papers, you note the child was a term, appropriate-for-gestational-age vaginal delivery with a birth weight of 3200 g (7 lb, 1 oz). Apgar scores were 9 at 1 and 5 minutes. Your examination is significant for a large firm mass on the right clavicle; the rest of the examination is normal. Management of this problem should include which of the following?
a) Immediate surgical excision
b) Ultrasound-guided biopsy
c) Reassurance and observation
d) Magnetic resonance imaging (MRI)