Etymology and terminology
The English word breast derives from the Old English word brēost (breast, bosom) from Proto-Germanic *breustam (breast), from the Proto-Indo-European base bhreus– (to swell, to sprout). The breast spelling conforms to the Scottish and North English dialectal pronunciations. The Merriam-Webster Dictionary states that "Middle English brest, [comes] from Old English brēost; akin to Old High German brust..., Old Irish brú [belly], [and] Russian bryukho"; the first known usage of the term was before the 12th century.A large number of colloquial terms for breasts are used in English, ranging from fairly polite terms to vulgar or slang. Some vulgar slang expressions may be considered to be derogatory or sexist to women. Evolutionary development
Humans are the only mammals whose breasts become permanently enlarged after sexual maturity (known in humans as puberty). The reason for this evolutionary change was unknown. Several hypotheses have been put forward:
A link has been proposed to processes for synthesizing the endogenous steroid hormone precursor dehydroepiandrosterone which takes place in fat rich  regions  of the body like the buttocks and breasts. These contributed to human brain development and played a part in increasing brain size. Breast enlargement may for this purpose may have occurred as early as Homo ergaster (1.7-1.4 MYA). Other breast formation hypotheses may have then taken over as principal drivers.It has been suggested by zoologists Avishag and Amotz Zahavi  that the size of the human  breasts can be explained by the handicap theory of sexual dimorphism.
The oral doses must be double the intravenous (IV) mesna dose due to bioavailability issues. The oral preparation allows patients to leave the hospital sooner, instead of staying four to five days for all the IV mesna infusions. Mechanism of action
Mesna reduces the toxicity of urotoxic compounds that may form after chemotherapy administration. Mesna is a water-soluble compound with antioxidant properties, and is given concomitantly with the chemotherapeutic agents cyclophosphamide and ifosfamide. Mesna concentrates in the bladder where acrolein accumulates after administration of chemotherapy and through a Michael addition, forms a conjugate with acrolein and other urotoxic metabolites. This conjugation reaction inactivates the urotoxic compounds to harmless metabolites. The metabolites are then excreted in the urine. Names
It is marketed by Baxter as Uromitexan and Mesnex. The name of the substance is an acronym for 2-mercaptoethane sulfonate Na (Na being the chemical symbol for sodium). See also
Coenzyme M—a coenzyme with the same structure used by methanogenic bacteria

References
External links
BC Cancer Agency
NIH/MedlinePlus patient information
Mesna at the US National Library of Medicine Medical Subject Headings (MeSH)