p27Kip1 is a key cell cycle gatekeeper governing the timing of Cyclin-dependent kinase (CDK) activation/inactivation and, consequently, cell proliferation. Structurally, the protein is largely unfolded, a feature that strongly increases its plasticity and interactors and enhances the number of regulated cellular processes. p27Kip1, like other intrinsically unstructured proteins, is post-translationally modified on several residues. These modifications affect its cellular localization and address p27Kip1 for specific interactions/functions. Several germline or somatic CDKN1B (the p27Kip1 encoding gene) mutations have been demonstrated to be associated with multiple endocrine neoplasia type 4 (MEN4), hairy cell leukemia, small-intestine neuroendocrine tumors, and breast and prostate cancers. Here, we analyzed the effect of four CDKN1B missense and nonsense mutations found in patients affected by MEN4 or cancers, namely, c.349C>T, p.P117S; c.397C>A, p.P133T; c.487C>T, p.Q163*; and c.511G>T, p.E171*. By transfecting breast cancer cell lines, we observed increased growth and cell motility for all the investigated mutants compared to wild-type p27Kip1 transfected cells. Furthermore, we discovered that the mutant forms exhibited altered phosphorylation on key residues and different localization or degradation mechanisms in comparison to the wild-type protein and suggested a possible region as crucial for the lysosome-dependent degradation of the protein. Finally, the loss of p27Kip1 ability in blocking cell proliferation was in part explained through the different binding efficiency that mutant p27Kip1 forms exhibited with Cyclin/Cyclin-dependent Kinase complexes (or proteins involved indirectly in that binding) with respect to the WT.

Multiple endocrine neoplasia type-4 (MEN4) is a rare form of multiple endocrine neoplasia due to a pathogenic variation in the cyclin-dependent kinase inhibitor 1B (CDKN1B) gene. It has a similar presentation to patients with multiple endocrine neoplasia type-1 (MEN1), with primary hyperparathyroidism and pituitary adenomas being the most common features. In this case, we describe a 54-year-old woman presenting with a pituitary macroadenoma cosecreting growth hormone and prolactin and primary hyperparathyroidism. She was initially managed with cabergoline without satisfactory response. Eventually she proceeded to transsphenoidal pituitary resection of the adenoma, and histology revealed appearances consistent with a mixed somatotroph-lactotroph adenoma. Subsequently genetic analysis confirmed the presence of a pathogenic variant in the CDKN1B gene (CDKN1B c.410del), in keeping with a diagnosis of MEN4. This is the first case of a cosecreting pituitary macroadenoma to be described in a patient with MEN4.

Multiple endocrine neoplasia type 4 (MEN4) is caused by a germline CDKN1B deleterious variant. CDKN1B encodes p27Kip1, a cyclin-dependent kinase inhibitor that acts as tumor-suppressor. Clinical presentation of MEN4 is similar to multiple endocrine neoplasia type 1 (MEN1) but the diagnosis of MEN4 can only be established once a germline CDKN1B pathogenic variant has been confirmed. We describe a unique case presenting with two -rare endocrine conditions. A 59-year-old female patient was diagnosed with medullary thyroid cancer (MTC) without evidence of a germline pathogenic variant in the RET proto-oncogene. Five years later, she developed Cushing's disease. A heterozygous germline variant was identified in the CDKN1B gene, specifically c.536del (p.Prol179GlnfsTer46), corresponding to a single-nucleotide deletion at position 536. This variant induces a frameshift, leading to an alternative stop codon. Immunostaining of the pituitary and thyroid tumors revealed a weak nuclear expression of p27/Kip1 without significant differences of expression between tumor and non-tumoral tissues. The NGS panel (Oncomine Comprehensive Assay v3) performed in both MTC and pituitary tissues identified the germline CDKN1B variant, as well as a pathogenic missense somatic variant c.182 A > G, p.(Gln61Arg) in HRAS in the MTC, without any RET somatic pathogenic variant. Evaluation of loss of heterozygosity (LOH) in both MTC and pituitary tissues showed compatibility with copy-neutral LOH, although further evidence is required for definitive confirmation. In conclusion, we report a clinical case of MTC coexisting with MEN4 due to a novel CDKN1B germline heterozygote frameshift variant.

Meningiomas are the most common primary brain tumors in adults but much less frequent in children. Many subtypes exist, including anaplastic (malignant) meningioma, which accounts for less than 20% of pediatric tumors. Meningiomas can arise in association with cancer predisposition syndromes due to germline variants in genes such as NF2, MEN1 and SMARCE1. This report describes a 6-year-old boy diagnosed with anaplastic meningioma who was treated with surgery and focal radiation therapy. The family consented to participate in the Texas KidsCanSeq clinical genomics study. Analysis of germline and tumor samples detected a single germline finding of a CDKN1B pathogenic frameshift variant associated with Multiple Endocrine Neoplasia Type 4 (MEN4) without somatic loss of the other allele. Tumor analysis revealed a YAP1::MAML2 fusion, which has been previously reported in pediatric meningiomas not associated with NF2. YAP1::MAML2 fusion is a known driver for development of meningioma, but the role of the germline CDKN1B variant in the absence of a tumor second hit is unclear. This case highlights the importance of performing combined tumor and germline molecular genetic analysis of rare tumors to help clarify the risk of development of cancer in patients with rare cancer predisposition syndromes.

Syndromic primary hyperparathyroidism has several features in common: younger age at diagnosis when compared with sporadic primary hyperparathyroidism, often synchronous or metachronous multi-glandular involvement, higher possibility of recurrence, association with other endocrine or extra-endocrine disorders, and suggestive family background with autosomal dominant inheritance. Hyperparathyroidism in multiple endocrine neoplasia type 1 is the most common syndromic hyperparathyroidism. It is often asymptomatic in adolescents and young adults, but may be responsible for recurrent lithiasis and/or bone loss. Hyperparathyroidism-jaw tumor syndrome is less frequent, but often immediately symptomatic, with higher blood calcium levels, and is sometimes associated with an atypic parathyroid tumor or parathyroid carcinoma. Hyperparathyroidism in multiple endocrine neoplasia type 2A is not at the forefront of the clinical picture, rarely revealing the disease, and often manifests with few symptoms. Multiple endocrine neoplasia type 4 is a more recently described entity, in which hyperparathyroidism seems to occur later and be less severe than in previous syndromes. In all cases, the indications and modalities of surgical treatment should be discussed in an expert center. The risk of recurrence after surgery, particularly high in multiple endocrine neoplasia type 1, requires long-term monitoring.