What Is The Difference Between Prognosis & Diagnosis?

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When it comes to the world of medicine, there are many terms that might seem confusing upon our first listen. Prognosis and diagnosis are two common examples of this. Both of these words are used when talking about health issues, including cancer, and are often confused due to their similarities. To put it simply, a diagnosis is an answer to “What do I have?”, whereas a prognosis is an answer to “What is my chance of survival?”. Here, we'll cover in detail the difference between the two and how they can impact they can be used in relation to cancer.


What Is A Diagnosis?

A diagnosis involves identifying the specific problem or disease that is present. It is a recognition of the current state and symptoms, and allocating a cause. 

In medicine this is usually done by an appropriately qualified practitioner, using various sources of information in order to classify a health problem, usually choosing from pre-existing categories and following specific medical guidelines. A diagnosis is required before a prognosis can be made and is used to inform the prognosis and appropriate treatment.


What Is A Prognosis?                                                              

A prognosis is a forecast or prediction. Medically, it is the likely outcome of the disease that you were diagnosed with. It is a prediction of how the disease is likely to go for you, or how the diagnosis will affect you in the future, and helps you to understand the seriousness and chances of survival. 

Statistics and research are used to inform a prognosis. While your doctor cannot actually know what will happen with your cancer, they can make an educated guess based on the experience of others in a similar situation. 

How Is Cancer Diagnosed?

Unfortunately, there is currently no one test that can diagnose cancer on its own. Most people will present with a concerning symptom, or undergo a screening test, at which point your doctor will need to engage in further enquiry. However, many people do not present with symptoms. Sometimes cancer is an incidental finding when performing a test for a separate issue or condition. 

Ways of getting more information include a medical history, physical examination, lab tests, imaging tests (scans), an endoscopy, or a biopsy (the only way to confirm cancer). Your doctor will use a variety of diagnostic methods to either exclude or arrive at a cancer diagnosis. If you are diagnosed with cancer, further assessment may need to be done to figure out the details and prognosis. 


Which Factors Can Influence Prognosis?

There are many factors that may affect a cancer prognosis. These include your general health, your age, sex, race, the type and location of the cancer, the stage (size and spread) and grade (how the cells look) of the cancer, cell traits, treatment response, and more. 

Survival Rates

When it comes to a cancer prognosis, your doctor will evaluate statistics about people who have had the same type of cancer. Cancer survival rates describe the percentage of people who survive a specific type of cancer over a period of time (a five year rate is often used, but the time period can vary). 

Sometimes the research will be more detailed, allowing for more specific comparison to your case. Rates can be used to understand prognosis, using the experience of others to imagine how you might respond. Combined with your specific goals, rates can also assist in the development of a treatment plan. 

Survival rates are explained or categorised differently depending on the source of the reporting. Some commonly used survival statistics include:

  • Overall (people of all ages and health conditions diagnosed with a certain cancer)
  • Disease-free (percentage who have no evidence of cancer after treatment)
  • Recurrence-free/Progression-free (percentage who show no signs of recurrence, or cancer that has not grown)

Cancer statistics are usually grouped according to stage and type, however research sources can vary in their methods of categorising statistics. For example, the SEER database groups cancers into ‘localized’, ‘regional’ and ‘distant’, instead of by AJCC TNM stages.

Outdated Statistics 

Survival statistics are generally at least 5 years old, which means that treatments and outlooks may have changed since. Newer treatments would not have had enough time to assess long-term outcomes and trends. Another issue is that survival rates are often grouped by stage of certain cancer, without taking into account factors such as age, overall health, tumour grade, etc. 

It is important to note that most survival statistics are treatment comparisons, which means that if you decide not to treat the cancer, it may be more difficult for your doctor to provide an accurate prognosis. In short, no two people are exactly alike and while statistics can help you to get more information on a potential outcome, they cannot predict your personal journey.

Cure vs Remission

A cure would mean that there is no sign of your cancer post-treatment and that it will never return. Remission involves reduced cancer symptoms and indicators, and can be partial or complete (the latter being when all cancer indicators are absent). 

Sometimes practitioners will refer to you as cured if you stay in complete remission for 5 years or more. However, it is important to know that cancer cells can stay in your body for many years, and may one day cause the cancer to return, making it difficult to call somebody cured with any certainty. Monitoring is the best way to keep track of a possible return or any delayed side effects from treatments.


Do I Want To Know My Prognosis?

A prognosis involves survival predictions and statistics, some of which can be scary or overwhelming. It can help decide on the best course of action and prepare for the journey, but it is a personal choice whether you want to know your prognosis, or even how much of it you want to be informed about. 

Some people find it easier to handle their journey when they know as much as possible about their cancer and likely outcomes. Others find little connection to data and prefer to approach their cancer from a unique and personal perspective.

Your diagnosis, prognosis, and treatment plan should be specific and unique to you, taking a whole-person approach.  Speak to someone today about your concerns and let them help you to feel more clear and confident in your health decisions.

Typically, a prognosis is expressed using general terms such as poor, favourable, moderate, excellent, excellent, fair, or hopeless.

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