Bradycardia (also sinus bradycardia) is a slow resting heart rate, commonly under 60 beats per minute (BPM) as determined by an electrocardiogram. It is considered to be a normal heart rate during sleep, in young and healthy or elderly adults, and in athletes.In some people, bradycardia below 60 BPM may be associated with fatigue, weakness, dizziness, sweating, and fainting. The term "relative bradycardia" is used to refer to a heart rate slower than an individuals typical resting heart rate. Athletes may have athletic heart syndrome, which includes bradycardia as part of the cardiovascular adaptations to training and participation.The word "bradycardia" is from the Greek βραδύς bradys "slow", and καρδία kardia "heart". Classification
Sinus
Atrial bradycardias are divided into three types. The first, respiratory sinus arrhythmia, is usually found in young and healthy adults. Heart rate increases during inhalation and decreases during exhalation. This is thought to be caused by changes in the vagal tone during respiration.Sinus bradycardia is a sinus rhythm of less than 60 BPM. It is a common condition found in both healthy individuals and those considered well-conditioned athletes. Studies have found that 50–85% of conditioned athletes have benign sinus bradycardia, as compared to 23% of the general population studied. The heart muscle of athletes has a higher stroke volume, so requires fewer contractions to circulate the same volume of blood.The third, sick sinus syndrome, covers conditions that include severe sinus bradycardia, sinoatrial block, sinus arrest, and bradycardia-tachycardia syndrome (atrial fibrillation, atrial flutter, and paroxysmal supraventricular tachycardia).
A hormone-receptor-positive (HR+) tumor is a tumor which consists of cells that express receptors for certain hormones. The term most commonly refers to estrogen receptor positive tumors (i.e. tumors that contain estrogen receptor positive cells), but can also include progesterone receptor positive tumors. Estrogen-receptor-positive tumors depend on the presence of estrogen for ongoing proliferation. Classification
ER-positive is one of the Receptor statuses identified in the classification of breast cancer. Receptor status was traditionally considered by reviewing each individual receptor (ER, PR, her2) in turn, but newer approaches look at these together, along with the tumor grade, to categorize breast cancer into several conceptual molecular classes that have different prognoses and may have different responses to specific therapies. DNA microarrays have assisted this approach. Diagnosis
Treatment
Endocrine treatment may be beneficial for patients with hormone receptor positive breast tumors.There are two ways for treating these kind of tumors: 

Lowering systemic levels of estrogen, achieved by the use of drugs from the aromatase inhibitor category. These drugs target one of the enzymes that takes part in the biosynthesis of estrogen. Blockage of the estrogen receptors on the cancerous cells, thus preventing estrogen binding, leading to decreased proliferation. Drugs in this category are also referred to as SERMs (Selective estrogen receptor modulator) since they are able to block estrogen receptors in a selective manner. See also
Tamoxifen
Raloxifene
Triple-negative breast cancer

References
Further reading
http://www.breastcancer.org/treatment/hormonal/what_is_it/hormone_role.jsp