A woman with stage-0 ductal carcinoma in situ (DCIS)—a non-invasive form of breast cancer—can end up needing a mastectomy, while her girlfriend, who has stage-1 invasive disease, gets to have just a lumpectomy and save her breast. This doesn't seem fair or logical, but it can happen. Why is this so?

The answer is related to the size of the cancers.

Stage-1 tumors are less than 2 centimeters across and so are very responsive to a lumpectomy followed by radiation. On the other hand, a stage-0 breast cancer—even though it's non-invasive and is contained within the duct—can occupy such a large area of the breast that a lumpectomy would look cosmetically unsightly, and so mastectomy becomes the solution.

Surgeons will tell you, though, that they would rather see someone with DCIS than someone with invasive disease, simply because the DCIS can't spread at this stage and isn't going to endanger her life. This underlines the value of mammography, which can catch a cancer when it's just a cluster of microcalcifications and not yet an invasive disease.

The moral? Rather than focus on what's fair and what's not, remember that both stages are detectable through early diagnosis and, with treatment, women usually do very well.