A prognosis is the doctor's best estimate of how cancer will affect a person, and how it will respond to treatment.
A prognostic factor is an aspect of the cancer or a characteristic of the person that may play a role in the prognosis. A predictive factor influences how a cancer will respond to a certain treatment. Prognostic and predictive factors are often discussed together and they both play a part in developing a treatment plan and a prognosis.
Many factors can affect a person's prognosis. Some of the most important prognostic and predictive factors are related to the specific cancer. They may include the:
- type of cancer
- subtype of cancer
- The subtype is based on the type of tissue or cells (histology).
- size of the tumour
- location of the cancer
- Cancer that has spread to the lymph nodes or to a distant site in the body generally has a less favourable prognosis than cancer that is confined to the location or organ where it first started to grow.
- gradegradeA description of a tumour that includes how different the cancer cells look from normal cells (differentiation), how quickly the cancer cells are growing and dividing, and how likely they are to spread. of the cancer
- stagestageA description of the extent of cancer in the body, including the size of the tumour, whether there are cancer cells in the lymph nodes and whether the disease has spread from its original site to other parts of the body. of the cancer
Other factors that may affect prognosis include:
- the person's age and sex
- the person's overall health
- presence of other medical conditions
- presence of specific symptoms related to the cancer, such as:
- weight loss
- swelling (edema)
- particular characteristics of the cancer, such as:
- depth of invasion
- growth pattern of the tumour (such as papillary versus solid)
- pattern of invasion (evidence of cancer spread to nerves, blood vessels or lymphatic vessels)
- presence or absence of tumour markers
- presence of abnormal chromosomes
- the person’s ability to carry out daily activities (performance status)
- Performance status is measured using different scales, which reflect the extent of the disease and how it may affect a person's ability to tolerate treatment. Examples of performance status scales include:
- Karnofsky Performance Status scale
- Eastern Cooperative Oncology Group (ECOG) scale
- World Health Organization (WHO) scale
- response to treatment
Favourable prognostic factors can have a positive influence on outcome. Unfavourable prognostic factors can have a more negative influence on outcome.
Generally, the earlier cancer is detected and treated, the better the outcome or prognosis. Cancer does not always do what it is expected to do. Because of this, it is difficult for doctors to determine a prognosis with any certainty. A prognosis can also change over time.