Spontaneous regression of tumors post-chemotherapy in a patient with relapsed small cell lung cancer: a case report.

BACKGROUND

Spontaneous regression (SR) of small cell lung cancer (SCLC) is an extremely rare phenomenon, and its underlying mechanisms remain unclear. Previous reports have suggested that immune-related factors, including paraneoplastic neurological syndrome (PNS) and anti-Hu antibodies, may be involved. In this report, we present a case of SCLC that demonstrated SR after initial progression, and explore the potential immunological mechanisms, particularly focusing on changes in the tumor microenvironment.

CASE DESCRIPTION: A 78-year-old Japanese male with a significant smoking history presented with two pulmonary nodules. Surgical resection revealed non-small cell lung cancer (NSCLC) and SCLC (stage IA2). Seven months later, SCLC recurrence was confirmed via transbronchial needle aspiration (TBNA) of the subcarinal lymph nodes. First-line chemotherapy with carboplatin and etoposide resulted in a good response; however, disease progression was observed later. Second-line treatment with carboplatin and nanoparticle albumin-bound (nab)-paclitaxel was initiated, but therapy was then discontinued because of declining performance status. Unexpectedly, without further treatment, the tumor and serum gastrin-releasing peptide precursor (pro-GRP) levels began to decrease over 6 months, indicating SR. Immunohistochemical analysis revealed an increase in cluster of differentiation (CD) 8-positive T cells and a decrease in regulatory T cells in the recurrent tumor, thus suggesting immune modulation.

CONCLUSIONS

This case of SCLC showed SR following chemotherapy, which was likely influenced by immune-related mechanisms. Changes in the tumor microenvironment, particularly an increase in cytotoxic T cells and a reduction in regulatory T cells, may contribute to SR. Nab-paclitaxel may contribute to the modulation of the tumor immune microenvironment. Therefore, understanding these mechanisms could provide insights into tumor immunity and potential therapeutic strategies.