What is the best treatment for pT2 cN1 seminoma with mild elevation of B-HCG (~100)?

I would recommend making sure that the pathology is seminoma (with either review of the orchiectomy specimen and making sure there are trophoblastic elements or a biopsy of the retroperitoneal lymph node) as the beta hCG level is getting close to the upper end of what I would expect from a seminoma. A PET-CT scan may be helpful as well to make sure there are no other areas of disease.

As for treatment, it would depend on the patient's anatomy (especially the proximity of the enlarged lymph node to one of the kidneys), but I would most likely favor radiation therapy over chemotherapy in a stage IIA setting. I usually treat with an ipsilateral dogleg field followed by a boost to the enlarged lymph node. If the patient is young, proton therapy ...

Mild elevation of HCG can happen from benign trophoblastic elements and would reduce after orchiectomy.

Assessing pathology to look for the benign elements will also help in confirming.

If the above is confirmed then would treat like seminoma and the option could be RT alone or like recent SAKK data of single agent carbo with involved site RT Papachristofilou et al., PMID 36228644.