Abstract
IntroductionLuminal, estrogen receptor-positive (ER+) breast cancers can metastasize but lie dormant for years before recurrences prove lethal. Understanding the roles of estrogen (E) or progestin (P) in development of luminal metastases or in arousal from dormancy is hindered by few preclinical models. We have developed such models.MethodsImmunocompromised, ovariectomized (ovx’d) mice were intracardiac-injected with luminal or basal human breast cancer cells. Four lines were tested: luminal ER+PR+ cytokeratin 5-negative (CK5−) E3 and MCF-7 cells, basal ER−PR−CK5+ estrogen withdrawn-line 8 (EWD8) cells, and basal ER−PR−CK5− MDA-MB-231 cells. Development of micrometastases or macrometastases was quantified in ovx’d mice and in mice supplemented with E or P or both. Metastatic deposits were analyzed by immunohistochemistry for luminal, basal, and proliferation markers.ResultsER−PR− cells generated macrometastases in multiple organs in the absence or presence of hormones. By contrast, ovx’d mice injected with ER+PR+ cells appeared to be metastases-free until they were supplemented with E or E+P. Furthermore, unlike parental ER+PR+CK5− cells, luminal metastases were heterogeneous, containing a significant (6% to 30%) proportion of non-proliferative ER−PR−CK5+ cells that would be chemotherapy-resistant. Additionally, because these cells lack receptors, they would also be endocrine therapy-resistant. With regard to ovx’d control mice injected with ER+PR+ cells that appeared to be metastases-free, systematic pathologic analysis of organs showed that some harbor a reservoir of dormant micrometastases that are ER+ but PR−. Such cells may also be endocrine therapy- and chemotherapy-resistant. Their emergence as macrometastases can be triggered by E or E+P restoration.ConclusionsWe conclude that hormones promote development of multi-organ macrometastases in luminal disease. The metastases display a disturbing heterogeneity, containing newly emergent ER−PR− subpopulations that would be resistant to endocrine therapy and chemotherapy. Similar cells are found in luminal metastases of patients. Furthermore, lack of hormones is not protective. While no overt metastases form in ovx’d mice, luminal tumor cells can seed distant organs, where they remain dormant as micrometastases and sheltered from therapies but arousable by hormone repletion. This has implications for breast cancer survivors or women with occult disease who are prescribed hormones for contraception or replacement purposes.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-014-0489-4) contains supplementary material, which is available to authorized users.
Highlights
Luminal, estrogen receptor-positive (ER+) breast cancers can metastasize but lie dormant for years before recurrences prove lethal
Their T47Dco origin was confirmed by short tandem repeat (STR) and karyotype analyses; their luminal versus basal-like classification and isogenicity were demonstrated by gene expression profiling [22]
estrogenderived line 3 (E3) cells are ER+progesterone receptor (PR)+; MCF-7 cells are ER+PR− in phenol red-free medium
Summary
Estrogen receptor-positive (ER+) breast cancers can metastasize but lie dormant for years before recurrences prove lethal. Despite progress toward early diagnoses and advances in treatment, 20% to 30% of all patients with breast cancer and 40% to 50% of patients with luminal breast cancer experience relapses that include distant metastases [3,4] This tends to occur within the first 5 years for patients with basal-like ER−PR− or HER2+ disease and later for patients with luminal disease [5]. The survival curve for luminal disease declines steadily after 5 years, overtaking more aggressive breast cancer subtypes after about 15 years [5,8]. Since they represent the most common forms of the disease, luminal tumors are responsible for most breast cancer deaths. Explanations for prolonged luminal tumor dormancy and their slow but inexorable recurrence and lethality remain unclear, and roles of cellular heterogeneity and hormones in this process, if any, are poorly understood
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