Embodiments disclosed herein generally relate to classifying a tumor, based on gene expression data, as being neurally related or non-neurally related. The tumor may be classified using a machine-learning model, which may have been trained to differentiate gene-expression data associated with neuronal or neuroendocrine tumors from gene-expression data associated with non-neuronal and non-neuroendocrine tumors. Differential treatment and/or treatment recommendations may be provided based on the classification. First-line checkpoint blockade therapy may be used or recommended when a tumor is identified as being non-neurally related, and a combination therapy (e.g., initial chemotherapy and subsequent checkpoint blockade therapy) may be used or recommended when a tumor is identified as being neurally related.