Histological classification of neoplasms
Pathological anatomy traditionally relies on the WHO International Histological Classification of Tumours (1979). According to this document, all pancreatic neoplasms are divided into several broad categories based on their tissue origin:
- Epithelial tumors. This is the most significant group, subdivided into benign (adenoma and cystadenoma) and malignant variants. The malignant range includes adenocarcinoma, squamous cell carcinoma, cystadenocarcinoma, acinar cell carcinoma, and undifferentiated carcinoma.
- Pancreatic islet tumors. Formed from the endocrine portion of the organ.
- Nonepithelial tumors. Develop from stromal elements.
- Mixed tumors. Combine elements of different tissues.
- Unclassified tumors. Neoplasms that cannot be assigned to a specific group.
- Hematopoietic and lymphoid tumors.
- Metastatic tumors. Secondary nodules seeded from other organs.
Morphology of benign tumors: cystadenoma
Among benign epithelial neoplasms, cystadenoma deserves special attention. This is a rather rare pathology with a very specific macroscopic and microscopic picture.
- Macroscopy: The tumor often reaches large sizes. On cross-section, it has a pronounced multilocular structure, presenting as a conglomerate of cystic cavities.
- Histology: The cavities of the cystadenoma are lined from the inside with epithelial cells. A crucial differential diagnostic feature is that this epithelium actively accumulates glycogen while not producing mucus at all.
- Instrumental diagnostics: During angiography, the picture changes depending on the study phase. In the arterial phase, the lesion appears as a well-vascularized area with a rich vascular network. In the parenchymal phase, the tumor shadow becomes heterogeneous, which is directly due to the presence of multiple fluid-filled cysts that do not accumulate contrast medium.
Pancreatic cancer: growth features and histogenesis
Malignant epithelial tumors can affect absolutely any part of the organ, but statistically they most frequently localize in the head.
- Cancer of the head: Macroscopically, the tumor presents as a very dense gray-white node. The borders of this node are indistinct, indicating an invasive growth pattern and invasion into surrounding healthy tissues.
- Cancer of the body and tail: Neoplasms in this localization frequently reach very significant sizes. This is explained by the fact that they grow completely asymptomatically for a long time. Unlike tumors of the head, they do not cause dysfunction of surrounding organs for a long time and do not obstruct vital ducts.
From the standpoint of histogenesis (tissue origin), malignant tumors of the exocrine portion are divided into two main types. If the tumor develops from the epithelium of the excretory ducts, adenocarcinoma forms. If the source of malignant growth becomes the acini of the excretory parenchyma, acinar (alveolar) carcinoma arises.
Pathogenesis of complications, metastasis, and outcomes
The localization of cancer in the head of the pancreas triggers a severe cascade of complications. The growing dense node first causes compression and then direct invasion of the walls of the pancreatic ducts themselves and the common bile duct.
Consequences of such growth:
- Impairment of normal pancreatic function due to blockade of secretion outflow, leading to the development of secondary pancreatitis.
- Liver dysfunction. Obstruction of the biliary tract causes cholangitis and subhepatic (obstructive) jaundice.
Routes of metastasis:
- Lymphogenous spread: This is the pathway for the first (early) metastases. Tumor cells settle in regional lymph nodes located directly adjacent to the head of the pancreas.
- Hematogenous spread: Characteristic of late stages of the disease. Via blood vessels, late metastases are seeded to the liver and other distant organs.
Death in pancreatic cancer most commonly results from severe body wasting (cachexia), the development of multiple life-incompatible metastases, or superimposed infectious complications, such as severe pneumonia.
Briefly: answers to topical questions
What types of hormonally active tumors develop from the pancreatic islets?
Among the hormonally active tumors described in the materials, VIPoma (Werner-Morrison syndrome) originates from pancreatic cells. It arises from D1 cells of the body and tail of the pancreas and synthesizes vasoactive intestinal peptide (VIP).
What precancerous epithelial changes precede the development of ductal pancreatic adenocarcinoma?
The development of pancreatic cancer is preceded by several types of precancerous epithelial lesions.
- Pancreatic intraepithelial neoplasias (PanIN) — glandular intraepithelial neoplasias of low grade and high grade.
- Intraductal papillary mucinous neoplasms (IPMN) — may be accompanied by low grade or high grade dysplasia.
- Mucinous cystic neoplasms (MCN) — are also subdivided into lesions with low- and high-grade dysplasia.
To easily remember the histogenesis of cancer, focus on the anatomy of the exocrine portion: excretory ducts give rise to adenocarcinoma, and terminal secretory units (acini) give rise to acinar cell carcinoma.
Class and exam questions
Why is cancer of the body and tail of the pancreas often detected at late stages?
In this anatomical zone, the tumor can grow completely asymptomatically for a long time. It does not compress the bile ducts or impair the function of surrounding organs, ultimately reaching significant sizes.
What complications are caused by the localization of cancer in the head of the pancreas?
The growing dense node inevitably compresses and then invades the common bile and pancreatic ducts. This leads to the development of secondary pancreatitis, cholangitis, and subhepatic (obstructive) jaundice.
Where does pancreatic cancer metastasize first?
The first metastases spread via the lymphogenous route. They affect regional lymph nodes located directly around the head of the pancreas.
How does a benign cystadenoma appear during angiography?
In the arterial phase, it is visualized as a well-vascularized formation. In the parenchymal phase, the tumor produces a heterogeneous shadow due to the presence of multiple cystic cavities.
What else to study on this topic
- Morphological differences between adenocarcinoma and squamous cell carcinoma of the pancreas.
- Pancreatic islet tumors: features of endocrine involvement.
- Nonepithelial and mixed neoplasms: histological picture.
- Pathogenesis of cachexia development in malignant tumors of the digestive system.
- Acute and chronic pancreatitis: morphology of inflammatory processes in the gland.
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