Uterine adenocarcinoma (endometrioid adenocarcinoma Type I)

Uterine adenocarcinoma or endometrial cancer (UA) is a common gynecological malignancy characterized by the transformation of cells of the endometrium, the inner epithelial lining of the uterus that consists of a layer of columnar luminal epithelium and tubular glands supported by a fibrovascular stroma. Generally, uterine adenocarcinoma begins as intraepithelial lesions that are quite invasive, leading to full invasive cancers involving the endometrial stroma. Subsequently a deeper penetration may occur in the myometrium leading to the engagement of lymphatic capillaries that spread the cancer to regional lymph nodes. Differently from high grade uterine adenocarcinoma that often metastasize, low-grade uterine adenocarcinoma tends to stay confined to the uterus, and this is important for the favorable prognosis (Ellenson et al., 2015; Mahdy et al., 2022).

About 90% of cases of uterine adenocarcinoma are sporadic and present morphological variants that can be summarized in two main types: type I (endometrioid adenocarcinoma) and type II (serous or clear cell adenocarcinoma) uterine adenocarcinomas (Bokham et al., 1983; Ryan et al., 2005).

Type I uterine adenocarcinoma are estrogen-related carcinomas that occur in pre- and post-menopausal women. They are frequently preceded by hyperplasia and usually have a good prognosis [Ryan et al., 2005; Creasman et al., 2006]. Endometrial hyperplasia is defined as an increased proliferation of endometrial glands relative to the stroma leading to an augmented ratio between gland and stroma when compared with the normal proliferative endometrium (Amant et al., 2005; Beral et al., 2005; Ellenson et al., 2015; Ottolina et al., 2015). Endometrial hyperplasia and endometrioid adenocarcinoma are associated with prolonged estrogenic stimulation of the endometrium, which may be caused by:

Anovulation and nulliparity, which have been associated with elevated risk for endometrial cancers (Yang et al., 2015);

Early menarche and late menopause, which can increase the time of exposure to endogenous estrogens, enhancing the risk for endometrial cancer (Kitson et al., 2017);

Obesity (peripheral conversion of androgens to estrogens) and hyperinsulinemia, a common factor associated with insulin-resistant type II diabetes, which lower the levels of SHBG (sex hormone binding globulin) resulting in higher blood levels of free estrogen (Setiawan et al., 2013; Ellenson et al., 2015);

Polycystic ovary syndrome and hypertrophic Leydig cells (characterized by an excessive functionality), which cause the production of androgen precursors which are converted to estrogens in adipose tissues (Papaioannou et al., 2010);

Estrogen replacement therapy (Ellenson et al., 2015).

Type II uterine adenocarcinoma differentiates from Type I since occur mainly in post-menopausal women; are not related to an excess of endogenous or exogenous estrogens and are usually not preceded by hyperplasia (Ryan et al., 2005).

Most common species used as model to study EC are rodents. Although some differences in gross anatomy of the female reproductive tract and reproductive cycle between humans and rodents exists, there are also common features that make this model biologically relevant to be representative of pathways relevant for EC in humans (Koebele and Bimonte, 2016; Treuting, 2017). Rodents have an estrous cycle occurring more frequently than humans (every 4-5 days against 28 days, respectively) and organized through four different phases (metestrus, diestrus, proestrus/ovulation and estrus rather than three (follicular, periovulatory/ovulation and luteal phase). Nevertheless, hormones and their fluctuation ruling the reproductive stage are to a certain extent similar in the way that the increased of 17b-estradiol levels preceding ovulation is followed by its decrease and concomitant progesterone rise (Koebele and Bimonte, 2016). Similar to humans, rodents experience age-related dysregulation of this cycle. Interpretation of reproductive aging in rodents is complicated by differences in age of cycle cessation, sequence of states in the transition period to anestrous (irregular cycle, persistent estrus, repeated pseudopregnancy) and consequent endocrine status in dependence on rats and mice strain (vom Saal et al., 1994; Koebele and Bimonte, 2016). Nevertheless, in rodents as in humans, aging involves progressive ovarian hormonal imbalance involving both 17b-estradiol and progesterone levels. As such, some strain of rodents (eg. Donryu rat) appear to develop uterine adenocarcinomas with features similar to EC in humans, occurring on a background of hyperplasia and elevation of 17b-estradiol

Animal models

OECD (2018), Test No. 451: Carcinogenicity Studies, OECD Guidelines for the Testing of Chemicals

Morphometric examination of the number of uterine gland profiles in representative transverse histological sections stained with the periodic acid-Schiff (PAS) procedure. Tumors are classified as adenocarcinomas of the uterus if derive from glandular endometrium and were invasive of the myometrium, the peritoneal cavity or beyond (Carthew et al. 2000).

Human histological classification

The International federation of Gynecology and Obstetrics (FIGO) 3-Grade Assessment of the Glandular Component, identifies three grades of endometrial cancer: Grade 1 is well differentiated, composed almost entirely of well-formed glands, and presents less than or equal to 5% solid non-squamous growth pattern; Grade 2 is moderately differentiated and characterized by 6%-50% solid non-squamous growth pattern; Grade 3 which is poorly differentiated and has more than 50% solid non-squamous growth pattern (Creasman et al., 2006; Ellenson et al., 2015);

Binary System: Type I endometrial cancer is usually a low-grade endometrioid carcinoma (it represents 80%-90% of all endometrioid carcinomas) (Ellenson et al., 2015; Mahdy et al., 2022) and is characterized by less than 50% myometrium invasion, absence of nuclear atypia and have a more favorable prognosis. Low-grade endometrioid carcinomas with more than 50% of myometrium invasion and high-grade endometrial cancer have poorer prognosis, presenting higher proportions of metastases and post-treatment recurrences (Creasman et al., 2006), resulting with only 46% 5-year survival rates (Lax et al., 2000).

There is no precise screening method for early detection of endometrial carcinomas. American Cancer Society guidelines emphasize the importance of reporting unexpected bleedings to their physician (Smith et al., 2002).

Transvaginal ultrasound may be a potential mean of early detection of endometrial carcinomas, but this measurement alone is not sufficient to define endometrial pathology. Saline infusion sonography and Color Doppler sonography were used to differentiate between endometrial cancer, endometrial hyperplasia, endometriosis, myoma or tamoxifen induced endometrial thickness (Achiron et al., 1995; Widrich et al., 1996). Other methods like magnetic resonance imaging, positron emission tomography or intraoperative ultrasound or three-dimensional sonography are not indicated for diagnosis but may be useful to gain information about the invasion depth of the myometrium or lymphatic metastases (Brosens et al., 1995; Teefey et al., 1996; Bonilla et al., 1997).

Uterine endometrioid adenocarcinoma is a progressive age-related human cancer disease defined by a multifactorial pathogenesis implicating both environmental and genetic factors. The application of this AOP is restricted to females and mammals.

In 2002, the World Health Organisation (WHO) through its International Programme for Chemical Safety, proposed a definition for endocrine disruptors (ED) and in 2009 a definition of adverse effects. Upon endorsement of those definition by the European Food Safety Authority, the Scientific Committee on Consumer Safety and the consensus of the scientific community, criteria for the determination of ED properties pursuant to Regulations (EU) No 528/20125 and (EC) No 1107/20096 have been set as defined in Commission Delegated Regulation (EU) No 2017/21007 and Commission Regulation (EU) No 2018/6058. According to these criteria, a substance shall be considered as having ED properties if accomplish all the following conditions:

a) it shows an adverse effect in [an intact organism or its progeny]/[non-target organisms], which is a change in the morphology, physiology, growth, development, reproduction or life span of an organism, system or (sub)population that results in an impairment of functional capacity, an impairment of the capacity to compensate for additional stress or an increase in susceptibility to other influences;

b) it has endocrine mode of action, i.e. it has the potential to alter the function(s) of the endocrine system;

c) the adverse effect is a consequence of the endocrine mode of action.”

Conclusions as to whether a substance meet the ED criteria must be drawn, as requested by Regulations (EU) No 528/20125 and (EC) No 1107/20096.

Uterine endometrioid adenocarcinoma is common outcome to hormones exposure (Henderson et al., 1982). Hormones, by promoting cell proliferation, allow accumulation of random genetic mutations due to DNA replication errors which may give rise to a malignant phenotype (Henderson et al., 1982). Epidemiological studies suggest potential roles for estrogenic EDs in increased risk of endometrial cancer, although the understanding of the direct role of EDs and the molecular mechanisms involved is still inconclusive (Gore et al. 2015).

Being the classification of endocrine disrupter (ED) a cut-off criteria for chemical substances used as pesticides and / or biocides, it appears of importance, in case of detection of uterine adenocarcinoma in the toxicology experiments necessary for authorization, to establish whether this effect is implemented through an endocrine-mediated mechanism.

Establishing a direct link between the occurrence of rodent EC due to ED exposure and an endocrine mode of action relevant to humans is difficult due to the multifactorial nature of carcinogenesis. It is thus necessary to establish the existence of a biologically plausible link between EC and endocrine activity.

The proposed AOP is addressing a regulatory endpoint represented by the increase in uterine weight (or uterotrophic response) that is elicited by ER agonists in animal models (Uterotrophic Bioassay in Rodents (UT assay) (OECD TG 440) and carcinogenicity studies (OECD TG 451).

Achiron, R., Lipitz, S., Sivan, E., Goldenberg, M., & Mashiach, S. (1995). Sonohysterography for ultrasonographic evaluation of tamoxifen-associated cystic thickened endometrium. Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine, 14(9), 685–688. https://doi.org/10.7863/jum.1995.14.9.685

Amant, F., Moerman, P., Neven, P., Timmerman, D., Van Limbergen, E., & Vergote, I. (2005). Endometrial cancer. Lancet (London, England), 366(9484), 491–505. https://doi.org/10.1016/S0140-6736(05)67063-8

Beral, V., Bull, D., Reeves, G., & Million Women Study Collaborators (2005). Endometrial cancer and hormone-replacement therapy in the Million Women Study. Lancet (London, England), 365(9470), 1543–1551. https://doi.org/10.1016/S0140-6736(05)66455-0

Bokhman J. V. (1983). Two pathogenetic types of endometrial carcinoma. Gynecologic oncology, 15(1), 10–17. https://doi.org/10.1016/0090-8258(83)90111-7

Bonilla-Musoles, F., Raga, F., Osborne, N. G., Blanes, J., & Coelho, F. (1997). Three-dimensional hysterosonography for the study of endometrial tumors: comparison with conventional transvaginal sonography, hysterosalpingography, and hysteroscopy. Gynecologic oncology, 65(2), 245–252. https://doi.org/10.1006/gyno.1997.4678

Brosens, J. J., de Souza, N. M., & Barker, F. G. (1995). Uterine junctional zone: function and disease. Lancet (London, England), 346(8974), 558–560. https://doi.org/10.1016/s0140-6736(95)91387-4

Carthew P, Edwards RE, Nolan BM, Martin EA, Heydon RT, White IN, Tucker MJ. Tamoxifen induces endometrial and vaginal cancer in rats in the absence of endometrial hyperplasia. Carcinogenesis. 2000 Apr;21(4):793-7. doi: 10.1093/carcin/21.4.793. PMID: 10753217.

Creasman, W. T., Odicino, F., Maisonneuve, P., Quinn, M. A., Beller, U., Benedet, J. L., Heintz, A., Ngan, H., & Pecorelli, S. (2006). Carcinoma of the Corpus Uteri. International journal of gynaecology and obstetrics: the official organ of the International Federation of Gynaecology and Obstetrics, 95 Suppl 1, S105–S143. https://doi.org/10.1016/S0020-7292(06)60031-3

Ellenson L.H., Pirog E.C. In: Robbins and Cotran Pathologic Basis of Disease. 9th ed. Kumar V., Abbas A.K., Aster J.C., editors. Elsevier/Saunders; 2015. The female genital tract; pp. 992-1022

Kitson, S. J., Evans, D. G., & Crosbie, E. J. (2017). Identifying High-Risk Women for Endometrial Cancer Prevention Strategies: Proposal of an Endometrial Cancer Risk Prediction Model. Cancer prevention research (Philadelphia, Pa.), 10(1), 1–13. https://doi.org/10.1158/1940-6207.CAPR-16-0224

Lax, S. F., Kurman, R. J., Pizer, E. S., Wu, L., & Ronnett, B. M. (2000). A binary architectural grading system for uterine endometrial endometrioid carcinoma has superior reproducibility compared with FIGO grading and identifies subsets of advance-stage tumors with favorable and unfavorable prognosis. The American journal of surgical pathology, 24(9), 1201–1208. https://doi.org/10.1097/00000478-200009000-00002

Mahdy, H., Casey, M. J., & Crotzer, D. (2022). Endometrial Cancer. In StatPearls. StatPearls Publishing.

OECD (2018), Test No. 451: Carcinogenicity Studies, OECD Guidelines for the Testing of Chemicals, Section 4, OECD Publishing, Paris, https://doi.org/10.1787/9789264071186-en.

Ottolina, J., Ferrandina, G., Gadducci, A., Scollo, P., Lorusso, D., Giorda, G., Breda, E., Savarese, A., Candiani, M., Zullo, F., & Mangili, G. (2015). Is the endometrial evaluation routinely required in patients with adult granulosa cell tumors of the ovary?. Gynecologic oncology, 136(2), 230–234. https://doi.org/10.1016/j.ygyno.2014.12.016

Papaioannou, S., & Tzafettas, J. (2010). Anovulation with or without PCO, hyperandrogenaemia and hyperinsulinaemia as promoters of endometrial and breast cancer. Best practice & research. Clinical obstetrics & gynaecology, 24(1), 19–27. https://doi.org/10.1016/j.bpobgyn.2008.11.010

Ryan, A. J., Susil, B., Jobling, T. W., & Oehler, M. K. (2005). Endometrial cancer. Cell and tissue research, 322(1), 53–61. https://doi.org/10.1007/s00441-005-1109-5

Setiawan VW, Yang HP, Pike MC, McCann SE, Yu H, Xiang YB, Wolk A, Wentzensen N, Weiss NS, Webb PM, van den Brandt PA, van de Vijver K, Thompson PJ; Australian National Endometrial Cancer Study Group, Strom BL, Spurdle AB, Soslow RA, Shu XO, Schairer C, Sacerdote C, Rohan TE, Robien K, Risch HA, Ricceri F, Rebbeck TR, Rastogi R, Prescott J, Polidoro S, Park Y, Olson SH, Moysich KB, Miller AB, McCullough ML, Matsuno RK, Magliocco AM, Lurie G, Lu L, Lissowska J, Liang X, Lacey JV Jr, Kolonel LN, Henderson BE, Hankinson SE, Håkansson N, Goodman MT, Gaudet MM, Garcia-Closas M, Friedenreich CM, Freudenheim JL, Doherty J, De Vivo I, Courneya KS, Cook LS, Chen C, Cerhan JR, Cai H, Brinton LA, Bernstein L, Anderson KE, Anton-Culver H, Schouten LJ, Horn-Ross PL. Type I and II endometrial cancers: have they different risk factors? (2013 ) J Clin Oncol. 31(20):2607-18. doi: 10.1200/JCO.2012.48.2596. Epub 2013 Jun 3. PMID: 23733771; PMCID: PMC3699726.

Smith, R. A., Cokkinides, V., von Eschenbach, A. C., Levin, B., Cohen, C., Runowicz, C. D., Sener, S., Saslow, D., Eyre, H. J., & American Cancer Society (2002). American Cancer Society guidelines for the early detection of cancer. CA: a cancer journal for clinicians, 52(1), 8–22. https://doi.org/10.3322/canjclin.52.1.8

Teefey, S. A., Stahl, J. A., Middleton, W. D., Huettner, P. C., Bernhard, L. M., Brown, J. J., Hildebolt, C. F., & Mutch, D. G. (1996). Local staging of endometrial carcinoma: comparison of transvaginal and intraoperative sonography and gross visual inspection. AJR. American journal of roentgenology, 166(3), 547–552. https://doi.org/10.2214/ajr.166.3.8623626

Widrich, T., Bradley, L. D., Mitchinson, A. R., & Collins, R. L. (1996). Comparison of saline infusion sonography with office hysteroscopy for the evaluation of the endometrium. American journal of obstetrics and gynecology, 174(4), 1327–1334. https://doi.org/10.1016/s0002-9378(96)70680-4

Yang, H. P., Cook, L. S., Weiderpass, E., Adami, H. O., Anderson, K. E., Cai, H., Cerhan, J. R., Clendenen, T. V., Felix, A. S., Friedenreich, C. M., Garcia-Closas, M., Goodman, M. T., Liang, X., Lissowska, J., Lu, L., Magliocco, A. M., McCann, S. E., Moysich, K. B., Olson, S. H., Petruzella, S., … Brinton, L. A. (2015). Infertility and incident endometrial cancer risk: a pooled analysis from the epidemiology of endometrial cancer consortium (E2C2). British journal of cancer, 112(5), 925–933. https://doi.org/10.1038/bjc.2015.24