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Summary
A mouse urinary bladder lesion, previously termed a mesenchymal tumor, may be a decidual-like reaction. This finding impacts risk assessment and clarifies the lesion's nature.
Area of Science:
- Veterinary Pathology
- Toxicology
- Cell Biology
Background:
- An unusual urinary bladder lesion in mice has been recognized for over 40 years.
- Its etiology, pathogenesis, biology, and classification remain debated among pathologists.
- Previous classifications include non-neoplastic epithelial lesion, smooth muscle cell tumor/leiomyosarcoma, and mesenchymal tumor.
Purpose of the Study:
- To investigate the etiology and classification of an unusual urinary bladder lesion in mice.
- To evaluate the hypothesis that the lesion represents a decidual-like reaction.
- To resolve the controversy between the "mesenchymal tumor" and "decidual-like reaction" classifications.
Main Methods:
- Histomorphologic analysis comparing the lesion to spontaneous uterine decidual reactions in mice.
- Evaluation of nuclear progesterone receptors, cytoplasmic granules, and resemblance to granulated metrial gland cells.
- Assessment of lesion reproducibility through long-term estrogen and progestogen administration.
Main Results:
- The lesion exhibits spindle and pleomorphic epithelioid cells with large, bizarre nuclei, mimicking malignancy.
- Histomorphologic similarities to uterine decidual reactions were observed.
- Presence of nuclear progesterone receptors, cytoplasmic granules, and resemblance to granulated metrial gland cells support the decidual hypothesis.
- Reproducibility with estrogen and progestogen feeding supports a hormonal influence.
Conclusions:
- The decidual-like reaction hypothesis provides a strong explanation for many features of the mouse urinary bladder lesion.
- Hormonal influence, specifically estrogens and progestogens, appears to play a role in lesion development.
- Resolving the classification debate is crucial for accurate risk assessment in toxicological studies.