The invention relates to compositions and methods for treating a patient having a tumor in order to reduce tumor size, comprising administering to the patient a replication-competent Paramyxoviridae virus comprising two or more of a) a nucleic acid sequence encoding a heterologous polypeptide, wherein upon administration the heterologous polypeptide is detectable in a biological fluid of the patient, and detection of the heterologous polypeptide is indicative of Paramyxoviridae virus growth in the patient and reduction in tumor size; b) a recombinant F protein, H protein, or M protein of Paramyxoviridae virus that increases fusogenicity of virus with cells; c) a nucleic acid sequence encoding a cytokine; and d) a Paramyxoviridae virus that is specific for cells of the tumor.