General characteristics of invasion
Invasive (infiltrating) growth is characterized by direct ingrowth of tumor cell complexes into surrounding structures with their subsequent destruction. The presence of such growth is one of the key signs of malignant transformation.
For instance, in malignant skin tumors with appendage differentiation, invasion manifests as the penetration of atypical epithelial cells deep into the dermis and subcutaneous adipose tissue. Such horizontal and vertical spread of the tumor is typically accompanied by the formation of indistinct, asymmetrical borders and foci of necrosis. Furthermore, as it grows, the tumor may involve lymphatic and blood vessels, which serves as a trigger mechanism for metastasis.
Manifestations of invasion in bone tissue
In bone pathology, invasive growth is inextricably linked with tissue destruction:
- Malignant osteoblastoclastoma: demonstrates extremely aggressive destructive growth. The neoplasm completely destroys the cortical layer of the bone and unhinderedly invades adjacent soft tissues, forming foci of necrosis and hemorrhages.
- Benign osteoblastoclastoma: despite a relatively favorable prognosis, this tumor is also capable of invasive destructive growth. Moreover, it is capable of metastasizing to the lungs, and its recurrence rate after removal reaches 10%.
- Malignant fibrous histiocytoma: is distinguished by the infiltrating growth of the tumor node, which is accompanied by severe pain syndrome and subsequent hematogenous metastasis.
In invasion in carcinomas using cervical cancer as an example
The development of cervical cancer allows us to clearly trace the staging of the invasive process. Carcinoma practically never arises on an unchanged background—it is always preceded by cervical intraepithelial neoplasia (CIN).
- Microinvasive carcinoma: this is the initial stage at which strands of anaplastic epithelium extend below the basement membrane. The depth of invasion here does not exceed 3 mm. However, even at such a minimal depth, vascular invasion is possible. Meanwhile, edema, fibroblast proliferation, and inflammatory infiltration are observed in the stroma.
- Invasive squamous cell carcinoma: a developed form characteristic of women aged 45–55. In the endophytic growth form (infiltrative or ulcerative), the tumor rapidly invades the surrounding cervical tissue. Further local invasion affects the walls of the urinary bladder and rectum. Tissue destruction leads to severe complications: the formation of rectovaginal and vesicovaginal fistulas, which entails septic conditions.
Growth features of germ cell tumors
Germ cell neoplasms (developing from sex and germ cells) are distinguished by an extremely malignant course and rapid, extensive dissemination.
Thus, a typical testicular seminoma (Chevassu's seminoma) may macroscopically appear as a moderately dense, demarcated multinodular formation. Nevertheless, it has a high potential for local spread: in approximately 50% of cases, the process involves the entire testis. In 10% of cases, tumor invasion into the epididymis and scrotal tissues is morphologically confirmed. Microscopically, the parenchyma proliferates in the form of solid extensive fields, narrow and broad strands, and its growth is accompanied by a pronounced granulomatous reaction and lymphoid infiltration.
To memorize the direction of local invasion and its complications in cervical cancer, use the "adjacent organs rule": the tumor grows forward and backward from the vagina into the urinary bladder (anteriorly) and into the rectum (posteriorly), forming respective fistulas leading to sepsis.
Class and exam questions
Does invasive growth always indicate an extremely unfavorable prognosis?
Not always. For instance, benign osteoblastoclastoma is capable of invasive destructive growth, but is characterized by a relatively favorable prognosis, even despite the risk of recurrence.
What is microinvasive carcinoma?
This is an early stage of invasion in which strands of atypical epithelium penetrate below the basement membrane to a strictly limited depth. For example, in cervical cancer, this depth does not exceed 3 mm.
How are invasion and metastasis connected?
Invasive growth is a mandatory prerequisite for dissemination. By invading the surrounding stroma, tumor complexes destroy the walls of blood and lymphatic vessels, penetrate their lumen, and are disseminated throughout the body.
What else to study on this topic
- Morphological criteria of malignancy: pronounced cellular atypia, polymorphism, and pathological mitoses.
- Histological variants of invasive squamous cell carcinoma (keratinizing and non-keratinizing types).
- Forms of local growth of neoplasms (exophytic, endophytic, papillomatous).
- Mechanisms of hematogenous, lymphogenous, and implantation metastasis.
- Differences between germ cell and non-germ cell tumors.
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