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The occurrence of more than one distinct form of an organism in a single life cycle.



an environmentally produced change in the incidence of disease and causes of death as well as in the properties of individual diseases, that is, nosologic entities (see NOSOLOGY).

During the 20th century, extensive immunization of populations and nationwide preventive measures in economically developed countries have eradicated many infectious diseases, for example, plague and poliomyelitis, and have sharply reduced infant mortality caused by infectious diseases. Changes in living conditions have reduced the incidence of diseases that stem from nutritional deficiency, for example, avitaminoses and iron-deficiency anemia. On the other hand, the incidence of injuries, tumors, and cardiovascular and viral diseases has increased.

New hereditary and occupational diseases have resulted from such environmental changes as those that accompany the growth of the chemical industry. Therapy-induced pleomorphism is a change in the clinical picture of a disease as a result of treatment. For example, the use of drugs has led to the disappearance of severe forms of thyrotoxicosis and anemia. Similarly, tuberculous meningitis, comas in diabetes mellitus, and acute pulmonary suppuration have become rare. In leukemia, tumor cells have disappeared from bone marrow because of the use of cytostatic agents, but they multiply in the nervous system and viscera. Undesirable side effects may follow medicinal treatment, and beyond a certain intensity these constitute a drug disease. The aftereffects of gastric or cardiac surgery, for example, can also give rise to disease.

Diseases that have received a new nosologic classification because of the growth of medical knowledge should not be considered examples of pleomorphism.


Davydovskii, I. V. Patologicheskaia anatomiia i patogenez boleznei cheloveka, 3rd ed., vols. 1–2. Moscow, 1956–58.
Shul’tsev, G. P. “Terapevticheskii patomorfizm.” Klinicheskaia meditsina. 1973, no. 6.
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References in periodicals archive ?
Monophasic lesions with pure, pleomorphic spindle cells only, such as monophasic metaplastic carcinoma, sarcomalike angiosarcoma, and malignant fibrous histiocytoma.
Pleomorphic variants are characterized by cellular heterogeneity with numerous larger cells with irregular nuclear contours.
Pleomorphic adenomas are generally slowly growing tumors that arise from salivary gland tissue in the superficial lobe of the parotid gland.
To establish the diagnosis of IDC-P in the loose cribriform and micropapillary patterns, other cytologic features are required, such as markedly enlarged and pleomorphic nuclei (>6 times that of adjacent nonneoplastic glands) and nonfocal comedonecrosis.
The results of fine-needle aspiration cytology (FNAC) were suggestive of a pleomorphic adenoma.
Based on the previously described findings, the diagnosis of pleomorphic (spindle and squamous cell) carcinoma arising in a mixed glandular and squamous papilloma was rendered.
In a recent report, Persson and colleagues (14) have postulated that 12q genes (in particular MDM2) may be a main target gene for malignant transformation in carcinoma ex pleomorphic adenoma.
Giant presentation of pleomorphic adenoma in major salivary gland.
Cyclin D1 and p16 expression in pleomorphic adenoma and carcinoma ex pleomorphic adenoma of the parotid gland.
PLGAs must be distinguished from pleomorphic adenomas and adenoid cystic carcinomas.
Invasive pleomorphic lobular carcinoma was first characterized by Dixon et al in 1982, (1) when he described a variant of invasive lobular carcinoma that did not fit one of the classic histologic patterns previously described.
Pleomorphic adenoma is rare in pediatric populations, where viral and congenital problems are the usual culprits responsible for submandibular masses.