Disclosed herein are methods of identifying and treating subjects with cancer, and methods of predicting a survival outcome in a subject with cancer, such as pancreatic cancer. In one aspect, the application provides methods for detecting the presence of cancer or infectious disease in a subject by collecting and analyzing sequencing information from the subject, such as by performing single cell RNA sequencing analysis of individual cells obtained from a sample from the subject. In a further aspect, the application provides methods for detecting the presence of cancer or infectious disease in a subject by determining microbial diversity and/or assessing the presence or absence of particular microbes in individual cells from the subject as compared to a control. Also provided are methods of determining T-cell microenvironment reaction, for example by sequencing nucleic acid molecules in individual T-cells obtained from the subject.