A 3-year-old girl is brought to the clinic by her mother, who tells you that the child has not been eating well over the past month and has developed swelling in the abdomen. On exam, the child has a smooth abdominal mass that is the size of a baseball on the left side. Vital signs reveal a blood pressure of 134/82 mm Hg, temperature of 99.8°F, and respirations of 16 breaths per minute. Urinalysis shows only 1+ red blood cells, and CBC and CMP are within normal limits.

What is the most likely diagnosis?
a. Nephroblastoma (Wilms tumor)
b. Renal cell carcinoma
c. Neuroblastoma
d. Mesoblastic nephroma