Tertiary lymphoid structures (TLS) develop in the human tumor microenvironment and correlate with prolonged survival. TLS are organized structures that resemble follicles of lymph nodes and contribute to local immune responses. Using immunofluorescence and quantitative pathology on human lung cancer and mouse lung samples, it was shown that TLS development followed sequential steps from simple lymphocytic aggregates to organized structures with lymphoid stromal cells and finally to mature TLS with a germinal center. Neoadjuvant chemotherapy and corticosteroid treatment significantly reduced the development of mature TLS, which was associated with poor outcome in patients with lung cancer. For details, see article by Siliņa and colleagues on page 1308.