What is the preferred systemic therapy regimen for a patient in their 40s with untreated metastatic sarcomatoid carcinoma of unknown primary, presenting with hepatic lesions, abdominal lymphadenopathy, and a lytic bone lesion?  

Molecular phenotyping. Two of three of my patients with this presentation this year (lots of nodes, no primary) turned out to be melanoma. The other one probably has a sarcomatoid recurrence of his remote 2014 renal cell carcinoma. A melanoma patient gets just immunotherapy for this presentation. ...