Is orchiectomy necessary for a patient with primary retroperitoneal seminoma and calcifications seen on testicular ultrasound (but no primary testicular mass)?  

For me, it depends. If the mass has a "sidedness" to it, I often recommend an ipsilateral orchiectomy. If the mass is midline and there is no dominant testicular mass, I just watch both testicles closely. In either case, I would incorporate exam and occasional testis ultrasound in followup.

No!