Spontaneous Regression of Bronchial Carcinoid Is Linked to a “Brisk” Tumor Lymphocytic Infiltrate

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To the Editor:
Spontaneous regression of cancer is a well-known phenomenon, its frequency is estimated to be about 1/100000 cancers, and some tumor types are more prone to unexpected regression (eg, melanoma, neuroblastoma, testicular germ cell tumor) than others (eg, carcinoma, lymphoma, sarcoma).1,2 Apoptosis, the immune system activity and the tumor microenvironment can explain this very rare event. In fact, a substantial body of research supports that the development of cancer is also influenced by the host immune system, underlying the importance of immunological biomarkers in predicting prognosis and response to therapy.3,4 For this reason, we have read with great interest the paper of Venkatram et al1 in which the authors have described the spontaneous regression of an endobronchial carcinoid tumor in a 67-year-old female patient, followed by serial bronchoscopies and biopsy over a 24-month period. Particularly, the well-assembled figure 3 shows the presence of several tumor-infiltrating lymphocytes besides to the neoplastic cells on hematoxylin and eosin stain.1 In this regard, our research group has investigated 45 surgical specimens (29 lung, 12 midgut, 4 pancreas) of well-differentiated (G1) neuroendocrine carcinoid tumors, in strict compliance with the World Health Organization criteria, with a follow-up period >10 years. We have found that a “brisk” tumor lymphocytic infiltrate correlates to a good prognosis, being the expression of an immunologic reaction to the neoplastic cells, with subsequent tumor regression. Conversely, a “nonbrisk” or absent infiltrate represents a form of immunotolerance to the tumor, favoring its growth and metastatic spread.5,6 From our findings, the quantitative immune score can be considered a prognostic indicator in carcinoid tumors7; thus, incorporating the immune score as a prognostic factor and introducing it into routine diagnostic assessment is advocated in the not-to-distant future.
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