Mandriota and colleagues reported the first experimental evidence that aluminum chloride concentrations within the range measured in the human breast can transform normal murine mammary epithelial cells (NMuMG) in vitro and cause tumor formation and metastasis in multiple mouse models. The study is in vitro and in vivo only; it does not involve human subjects, and extrapolation to human breast cancer requires epidemiological corroboration.
Key numbers
In vitro transformation (pp. 2782 to 2784)
NMuMG cells cultured 4 to 16 weeks with aluminum chloride at 100 micromolar showed morphological change from cobblestone to fibroblastoid, approximately 62 percent decrease in E-cadherin expression, and 3.7-fold increase in N-cadherin, markers consistent with epithelial-mesenchymal transition.
Soft agar colony assay: aluminum chloride-treated cells formed significantly larger colonies than controls. Original NMuMG cells: p equals 6.71 times 10 to the negative 4 (two-tailed t-test, Figure 2b). ATCC-sourced NMuMG cells at 10 micromolar: p equals 0.02; at 100 micromolar: p equals 2.79 times 10 to the negative 5 (Figure 2c).
In vivo tumorigenesis (pp. 2783 to 2789)
NSG model (most immunodeficient): aluminum chloride-treated cells produced 100 percent tumor incidence (5 of 5 mice), significantly larger tumors at 32 days (p less than 0.001, Figure 3a), and significantly larger lung metastases compared with controls. Tumor volumes diverged significantly by day 13 (p equals 0.02) and remained significant through day 45.
NOD SCID model: aluminum chloride-treated cells formed palpable tumors by day 14 (p equals 0.0049) in all 5 mice. Control NMuMG cells did not grow beyond the injection volume in the same period (Figures 6a and 6b, p. 2787).
Swiss nude model: aluminum chloride-treated cells formed significantly larger tumors. Control cells also formed tumors in this less immunodeficient model but were smaller.
Metastasis: 3 of 5 Swiss nude mice injected with aluminum chloride-treated cells had macroscopically visible lung metastases; control cells had none. NSG mice showed brain and liver metastases from aluminum chloride-treated cells; none in control-cell groups (Figure 5, p. 2788).
Aluminum concentration context (p. 2788)
Aluminum chloride at 100 micromolar equals approximately 2.7 micrograms per milliliter aluminum. Published human breast tissue aluminum concentrations cited by the authors: 150 to 520 micrograms per liter (mean 468.4 plus or minus 28.1); nipple aspirate fluids 5.6 to 19.3 micromolar; type I breast cysts 80 to 330 micrograms per liter (median 150, corresponding to 3.0 to 12.2 micromolar); breast tissue 4 to 437 nmol per gram dry weight (0.8 to 87 nmol per gram wet weight). The authors note that the 100 micromolar transforming concentration is within or very close to the range measured in the human breast.
Mutation analysis (p. 2787)
Whole-exome sequencing of aluminum chloride-treated versus control NMuMG cells found 48 mutations in 43 genes. Genes included regulators of proliferation, migration, metastasis, and apoptosis: Mnt and Tiam2 were among the most notable. Sanger confirmation rate: 92.8 percent. Transformation persisted after 5 weeks of aluminum chloride withdrawal, consistent with a mutagenic rather than purely epigenetic mechanism.
Methods (brief)
In vitro: NMuMG and MCF-10A cells (separately) cultured in standard conditions with aluminum chloride dissolved in Milli-Q water at 100 micromolar (and at 10 mM and 30 mM for preliminary runs). Soft agar colony assays at 2 times 10 to the 4 cells per mL, 14 days, colony diameters measured microscopically. Western blot for E-cadherin and N-cadherin. In vivo: 5 times 10 to the 6 PBS-washed cells injected subcutaneously into flanks of 6-week-old female mice in 200 microliters Matrigel; 5 mice per condition. Three mouse models: NSG (NOD SCID gamma), NOD SCID, and Swiss nude. Tumor volumes measured by caliper twice weekly. Tissue sections stained with hematoxylin and eosin. Whole-exome sequencing performed on treated versus control cell lines.
Evidence fitness
This source provides controlled experimental evidence that aluminum chloride concentrations within the range measured in human breast tissue can transform spontaneously immortalized murine mammary epithelial cells and produce tumor formation and metastasis in multiple mouse immunodeficiency models. It supports the biological plausibility of aluminum as a potential mammary carcinogen. It does not establish human breast cancer causation; NMuMG cells are murine and spontaneously immortalized, mouse models are not humans, and in vitro aluminum chloride exposure is not equivalent to dermal antiperspirant exposure. Risk quantification and translation to human exposure levels require epidemiological studies with dose and temporal data.
Limitations
Mouse and in vitro only. NMuMG cells are spontaneously immortalized; prior genomic instability may interact with aluminum treatment. NSG and NOD SCID mice lack immune effector cells that would normally suppress tumor formation. The effective concentration (100 micromolar) equals approximately 2.7 micrograms per milliliter, which is within the breast tissue range but is a sustained cell-culture exposure not equivalent to intermittent dermal deposition. Aluminum chloride was used as the test salt; aluminum chlorohydrate (the active in antiperspirants) was not used. No dose-response curve below 10 micromolar was established. Whole-exome sequencing of cell lines does not translate directly to carcinogenesis in intact tissue.
Related evidence
- Antiperspirant (Al-salt, dirty sibling of r9 deodorant)
- Aluminum
- Use of Underarm Cosmetic Products in Relation to Risk of Breast Cancer: A Case-Control Study
- The Potential Metalloestrogenic Effect of Aluminum on Breast Cancer Risk for Antiperspirant Users
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