Urinary incontinence is reported in 10-25% of women younger than the age of 65 years and in more than 50% of patients who are bedridden. Urinary incontinence may be exacerbated when estrogen levels are low.  Breast cancer patients with urinary incontinence may not initially report the problem voluntarily because issues related to the cancer assume a higher priority for them. Because urinary incontinence is sometimes related to a significant underlying pelvic pathology, it is important for the physician to inquire about this condition.

Multiple factors may contribute to incontinence, including older age; multiple vaginal births;  smoking;  neurologic,  gastrointestinal,  and pulmonary disease; genetic factors; and certain drugs-for example, antihypertensives,  dopaminergic agonists,  cholinergic agonists,  neuroleptics, adrenergic β-agonists, and xanthines.

The three major types of incontinence are stress incontinence,  urge incontinence, and overflow incontinence.

Stress Incontinence
True stress incontinence occurs when increased intra-abdominal pressure is transmitted equally to the bladder and the functional part of the urethra.  Stress incontinence is caused by loss of anatomic support of the urethra, bladder, and urethrovesical junction, which allows the urethra to be displaced below the pelvic floor. When intra-abdominal pressure in addition to intravesical pressure exceeds the urethral closing pressure,  involuntary loss of urine occurs.  The most common causes of stress incontinence are traumatic vaginal birth,  multiple pregnancies, and,  in menopausal women,  tissue atrophy secondary to decrease in periurethral vascularity and atrophy of the mucous membrane of the urethra.

Urge Incontinence
Urge incontinence, also known as detrusor instability, is characterized by involuntary loss of urine associated with an abrupt and strong desire to void. Urge incontinence is usually a chronic condition. It is caused by sudden, spontaneous contraction of the detrusor muscle of the bladder, which is thought to be triggered by uninhibited stimulation of detrusor muscle receptors.  Urine leakage may occur when the patient is in any position and is more frequent with changes in position. Also, patients with urge incontinence may report an inability to stop their urine stream during voiding.

Urge incontinence can be differentiated from stress incontinence on the basis of symptoms. Whereas stress incontinence usually disappears at night, urge incontinence is often associated with nocturia.

Sudden onset of urge incontinence in a patient diagnosed with breast cancer should raise suspicion of a bladder infection or a pelvic mass (associated with enlargement of the uterus or ovaries)  pressing on the bladder. A pelvic examination should reveal any such pelvic mass.