What does "prognostic significance" mean exactly?

Question

I am trying to more fully understand a pathologist report and do not know what "Prognostic Significance" means.

Example...

Estrogen Receptor
Result: 80% positive
Prognostic Significance: Favorable
Reference Range: > 1%

Answer 1

Although it would be helpful if we knew what sort of pathology report this was, I surmise that it is likely describing analysis of a biopsy or surgically removed tissue specimen from a breast cancer.

In breast cancer, it has long been known that some but not all tumors express hormone receptors, particularly estrogen and progesterone. Although the mechanism is complicated, the basic idea is that estrogen can bind to the cells in the tumor and make it grow faster. For this reason, people with tumors expressing the estrogen receptor are often treated with hormonal therapy that blocks that hormonal stimulation. In pre-menopausal women, this is usually tamoxifen or a related drug, which blocks the receptors directly. In post-menopausal women, a class of drugs called aromatase inhibitors (anastrozole, letrozole, etc.) that block estrogen production are used. The important piece to note is that only tumors that express estrogen receptors respond to this type of hormonal treatment.

Partly because of the availability of these hormonal treatments, and perhaps partly due to the biology of the tumors themselves, breast cancer that expresses estrogen receptors tends to have a better prognosis than estrogen-receptor negative breast cancer. Prognosis can refer to a variety of outcomes; in cancer studies it’s usually either survival or cancer-free survival. Patients with estrogen-receptor positive breast cancer tend to fare better than those with estrogen-receptor negative tumors. Another way of stating that is: the presence of the estrogen-receptor has a favorable prognostic significance.

The pathology report (if I’ve got the context correct!) is saying that most (80%) of the cells in the specimen expressed the estrogen receptor. It then comments that this is known to be a favorable finding.