Organ culture allows for the understanding of normal and tumor cell biology, and tissues generally remain viable for 5–7 days. Strikingly, we determined that myometrial and MED12 mutant leiomyoma cells repopulated cell-depleted tissue slices after 20 days of culture. Using immunofluorescence and quantitative PCR of stem cell and undifferentiated cell markers, we observed clusters of CD49b⁺ cells in tumor slices. CD49b⁺ cells, however, were sparsely detected in the myometrial slices. Almost all LM cells strongly expressed Ki67, while only a few myometrial cells were stained for this proliferation marker. The CD73 marker was expressed only in tumor cells, whereas the mesenchymal stem cell receptor KIT was detected only in normal cells. HMGA2 and CD24 showed broader expression patterns and higher signal intensity in leiomyoma than in myometrial cells. In this study, we propose that activating CD49b⁺ stem cells in myometrium leads to asymmetrical division, giving rise to transit-amplifying KIT⁺ cells that differentiate to smooth muscle cells. On the contrary, activated leiomyoma CD49b⁺ cells symmetrically divide to form clusters of stem cells that divide and differentiate to smooth muscle cells without losing proliferation ability. In conclusion, normal and mutant stem cells can proliferate and differentiate in long-term organ culture, constituting a helpful platform for novel therapeutic discovery.

Deregulated steroids are involved in different hormone-dependent tumors, including benign and malignant uterine neoplasms. Leiomyomas (LM) are estrogen and progesterone-dependent benign tumors, whereas “bizarre or atypical LMs” (AL) are considered a subgroup of LM and clinically benign, although their malignant potential is suspect. Uterine leiomyosarcomas (LMS) are malignant smooth muscle tumors, and ovarian steroids may control their growth. Estrogen effects are mediated by 2 receptors, estrogen receptors (ER) α and β, and the ratio of both receptors seems to be a critical parameter in the estrogen-mediated carcinogenic process. Estradiol induces the expression of neurotensin (NTS), and the coupling of this peptide with its high-affinity receptor, NTS1, has been involved in the regulation of tumoral cell growth. Given the importance of these markers in tumor development, we aim to determine the status of ERα and ERβ in the myometrium and LM, AL, and LMS, concomitantly with the expression of NTS/NTS receptor 1 in these tumors. For that purpose, we use immunohistochemistry for all markers analyzed and in-situ hybridization to detect NTS mRNA. These data suggest that LMS are estrogen-dependent tumors, which may use NTS as an autocrine growth factor. In addition, the phenotype of AL with regard to ERα and ERβ status and NTS expression is closer to LMS than LM; thus, a potential malignization of this tumor is feasible.

Uterine leiomyosarcoma (LMS) is a rare and aggressive malignancy with diagnostic challenges, particularly in cases with overlapping histological features with atypical leiomyoma or smooth muscle tumors of uncertain malignant potential. We report a comparative immunohistochemical analysis of LMS, leiomyoma, and adjacent myometrium obtained from a 40-year-old woman with discordant pathological diagnoses. LMS tissue showed increased Ki67 and NTS/NTSR1 immunoreactivity together with a distinctive cytoplasmic localization of estrogen receptor beta (ERβ), in contrast to the predominantly nuclear localization observed in leiomyoma and normal myometrium. Importantly, focal areas within adjacent morphologically non-neoplastic myometrium exhibited an immunophenotype resembling LMS, including cytoplasmic ERβ localization and increased Ki67 and NTS/NTSR1 expression. These observations suggest a potential association between ERβ subcellular localization, NTS/NTSR1 signaling, and molecular alterations occurring during uterine smooth muscle tumorigenesis. However, given the single-case nature of this report, these findings should be considered exploratory and require validation in larger studies. The diagnostic message conveyed by these images may assist in the interpretation of diagnostically challenging cases and provide a basis for future investigation.