Comparison with the tonsils shows that PALT displays immunomorphological features required for the onset of cellular and humoral immune responses, while its T regulatory cells appear to function as suppressor-regulators of T and B cell responses.

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Pulmonary carcinoids, distinct in typical and atypical, represent 2–5% of all primary lung tumors. The aim of this study was to investigate the molecular alterations correlated with the development of this form of neoplasms. A collection of 38 paraffin-embedded apparently sporadic carcinoids was investigated, through a combined study, for protein expression/localization of menin, p53, β-catenin and E-cadherin and for mutational analysis of the MEN1, TP53 and CTNNB1 genes. Menin was expressed in 71% of cases, with a prevalent cytoplasmic (c) localization, β-catenin was expressed in 68.4% of cases, of which 36.8% with a membranous (m) and 31.6% with a cytoplasmic localization. Membranous E-cadherin immunoreactivity was detected in 84.2% cases, nuclear p53 expression in 5.3% of cases. Positive correlation was found between c-menin and c-β-catenin expression (rho=0.439, P=0.008). In addition, m-β-catenin showed a positive correlation with both c-β-catenin and E-cadherin expression (rho=0.380, P=0.022 and rho=0.360, P=0.040, respectively). With regard to the E-cadherin/β-catenin complex, we found also a significant positive correlation between c-menin and ‘disarrayed’ β-catenin expression (rho=0.481, P= 0.007). MEN1 gene variants were characterized in 34% of cases. c-menin was more highly expressed in tumors with MEN1 variants, compared to tumors without MEN1 variants (P=0.023). Three nucleotide variants of TP53 were also detected. This study confirms the involvement of the MEN1 gene in the development of sporadic pulmonary carcinoids, demonstrates the accumulation of menin in the cytoplasm, and indicates that the disarrayed pattern of the complex significantly correlates with c-menin accumulation.

Mast cell leukemia (MCL) is the leukemic form of SM with at least 20% mostly immature mast cells on bone marrow aspirate. MCL may develop de novo, in the absence of a prior SM, or it may represent a progression from a previous SM. MCL may be sub-divided into the more frequent, aggressive acute form with signs of organ damage (C-findings) and the chronic form lacking C-findings and presenting a more stable course, although over time, progression to acute MCL is common. The 2022 WHO subtype of MCL with an associated hematological neoplasm was renamed MCL with an associated myeloid neoplasm in the 2022 International Consensus Classification (ICC). The relevance of the distinction between the leukemic and aleukemic forms based on the percentage of circulating mast cells is a matter of debate. The current knowledge on MCL is restricted mainly to single reports or case series with a limited number of larger studies. Our aim is to provide a comprehensive overview of this rare disease in terms of clinical manifestations, morphology, phenotype, molecular characteristics, differential diagnosis, outcome and treatment. A general overview on mastocytosis is also included.