Introduction
Neuroendocrine tumors are malignancies that originate in specialized cells known as neuroendocrine cells. Similar characteristics to neuron and hormone-producing cells are found in neuroendocrine cells. Although they are uncommon, neuroendocrine tumors can develop at any place in the body. The majority of neuroendocrine tumors arise in the lungs, small intestine, appendix, rectum, and pancreas. This article explains in detail about neuroendocrine tumors and their pseudo-progression.
What Are Neuroendocrine Tumors?
Neuroendocrine neoplasms (NENs) are diverse cancers with complicated histology. Widely distributed cells possessing both "neuro" and "endocrine" qualities are referred to as "neuroendocrine" cells. The "neuro" feature is based on the discovery of dense core granules (DCGs4), comparable to DCGs seen in serotonergic neurons and responsible for monoamine storage (neuroendocrine cells do not have connections, in contrast to neurons). A monoamine's synthesis and secretion are referred to as its "endocrine" properties.
The neuroendocrine (NE) system consists of dispersed cells in the exocrine parenchyma. It includes the endocrine tissues of the gastrointestinal and respiratory systems, which are part of the diffuse endocrine system, and the endocrine glands (like the pituitary, parathyroids, adrenal glands, and the endocrine tissues embedded inside glandular tissue (pancreatic or thyroid). Well-differentiated neuroendocrine neoplasms have historically been called carcinoid tumors.
Neuroendocrine tumors come in a variety of forms. Certain neuroendocrine tumors develop slowly, while others grow rapidly. Functional neuroendocrine tumors are those that overproduce hormones. Others, known as nonfunctional neuroendocrine tumors, either do not produce any hormones at all or do not have enough to cause symptoms. The type of tumor, its position, whether it produces extra hormones, how aggressive it is, and whether it has migrated to other parts of the body are all factors affecting how neuroendocrine tumors are diagnosed and treated.
What Are the Examples of Neuroendocrine Tumors?
PNETs (pancreatic neuroendocrine tumors), a type of endocrine tumor that develops in the pancreas, are the most common neuroendocrine tumors.
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Gastroenteropancreatic neuroendocrine tumors.
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Carcinoid tumors in the lungs.
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Metastatic neuroendocrine tumors.
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Large cell neuroendocrine carcinoma in the lungs.
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Neuroendocrine carcinoma in the pancreas or gastrointestinal tract.
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Small cell lung carcinoma.
What Are the Causes of Neuroendocrine Tumors?
The specific cause of neuroendocrine tumors is unknown. Neuroendocrine cells, which resemble nerve and hormone-producing cells, are the starting point of these tumors. The human body is full of neuroendocrine cells. When neuroendocrine cells experience DNA (deoxyribonucleic acid) alterations or mutations, neuroendocrine tumors start. The instructions that inform a cell what to do are encoded in its DNA. The alterations instruct the neuroendocrine cells to proliferate quickly and develop into a tumor. A small percentage of neuroendocrine tumors grow slowly. Aggressive cancers are those that either spread (metastasize) into various parts of the body or invade and destroy healthy bodily tissue.
How Common Is Neuroendocrine Tumor?
In children, neuroendocrine tumors are uncommon; in adults, they are more common. In adulthood, carcinoid tumors (slow-growing neuroendocrine tumors) are thought to impact 4 out of 100,000 people. There is little information available on the prevalence of neuroendocrine tumors in adolescents and young adults due to their rarity.
What Is Pseudoprogression in Neuroendocrine Tumors?
Immunotherapy (a kind of cancer treatment that boosts the body's defenses against the disease) has grown in popularity as a new basis for cancer treatment. Some aberrant response patterns, such as pseudoprogression and hyper progression are observed after immunotherapy. Pseudoprogression is a phenomenon wherein there is an initial increase in the size of the tumor or the appearance of new lesions, followed by a decrease in the tumor burden.
Patients undergoing immunotherapy may benefit from this phenomenon, but it frequently results in premature discontinuation of treatment due to an incorrect assessment of the tumor's progression. For doctors, accurately identifying pseudoprogression is another issue. Much progress has been accomplished as a result of the widespread attention that pseudoprogression has received. Several new criteria were developed to appropriately assess the response to immunotherapy.
What Is the Mechanism of Pseudoprogression After Immunotherapy?
The precise molecular process underlying pseudoprogression remains unclear despite a large amount of research on the subject. Magnetic resonance imaging (MRI) of the brain revealed extensive perilesional (around a lesion) edema and enlargement of lesions in the central nervous system in certain patients. An abundance of microglial cells, reactive astrocytosis, and scattered inflammatory cells surrounding isolated clusters of tumor cells in a resected left parietal-occipital lesion. These findings were consistent with the reaction to treatment rather than tumor progression. Pathologic examination of the liver lesions revealed severe necrosis and lymphohistiocytic infiltration. The primary process of pseudoprogression involves the invasion of immune cells, including macro phagocytes, CD4 T cells, and CD8 T cells, leading to edema and hemorrhage. Only very little research has concentrated on the clinical traits of individuals who experience pseudoprogression, even though the condition has received a lot of attention.
How Can Pseudoprogression Be Distinguished From True Progression?
There is currently no common identification standard for pseudoprogression, even though numerous investigations on the phenomenon following immune checkpoint inhibitor therapy have reported pseudoprogression in a variety of tumor types. Although they all have certain drawbacks, new assessment criteria, including irRC (immune-related response criteria), iRECIST (immune response evaluation criteria in solid tumors), and imRECIST (immune-modified response evaluation criteria in solid tumors), were suggested to more accurately detect pseudoprogression for tumor immunotherapy. The identification of pseudoprogression for immunotherapy in malignancies is a highly desirable goal, and the following section addresses some potentially helpful approaches to this end.
Conclusion
Neuroendocrine tumors are a rare type of tumor. It begins in specialized cells in the neuroendocrine system. Pseudoprogression is an unusual response seen not just in immunotherapy-treated tumors, but also in chemoradiotherapy-treated malignant gliomas and tyrosine kinase inhibitor-treated tumors. Pseudoprogression is a clinical condition that presents difficulties for patients and doctors.
