TNM Classification

TNM Classification

Most patients (but not all) will no doubt notice this collection of letters and additional letters or numbers in their lab results and health records. This is an international anatomically-based classification system for malignant tumours, which was devised by Pierre Denoix in the 1940s. The first TNM Classification was published in 1968 by the International Cancer Research Organization. Although doctors in Latvia are currently using the 7th edition of this classification system, the 8th edition was published on January 1, 2018. Three factors constitute the basis for this classification – the tumour, lymph nodes and metastases. There are tumours that, due to their unusual growth characteristics, cannot be classified according to the TNM system. In such cases, other popular classification systems such as FIGO, Dukes, Breslow and other methods are used.

The TNM classification doesn’t change over the course of the illness and it is only applied to solid tumour cancers. If there is any doubt about the degree of the tumour, then the milder version is applied. The TNM classification does not describe the biological nature of the tumour and similarly does not predict the tumour’s reaction to any given therapy. It only indicates the extent of the disease at the time it is being examined. As the new version of the TNM Classification recommends that we use more precise designations, then we must, if at all possible, adhere to this new version.

T = tumour

The tumour itself is designated with a capital T (tumor in Latin) and the degree next to this letter indicates the size of the tumour and whether or not it has invaded surrounding tissues (the skin, muscle or the layers of respective organs). The larger the number, the larger the tumour and the greater its dissemination to (invasion of) surrounding tissues. For example, T0 indicates that cancer cells were not found in the sample of the tissue that was examined. This is the judgement of the pathologist. It can also be that there are no cancer cells in the organ that was examined, yet metastases have been discovered in the regional lymph nodes. TX indicates that data are not available for the primary or original tumour. This can happen if, for example, an operation was conducted elsewhere and the documents were not saved. Tis indicates in situ or non-invasive carcinoma (see earlier blogposts), while T1-T2-T3-T4 indicate the size of the primary tumour and to what degree it has invaded surrounding tissues. For some tumours, T may also indicate something specific to that particular tumour.

The larger the tumour, the greater the likelihood that cancer cells have already migrated not only to the regional lymph nodes, but also further via the bloodstream. However, there have been cases, and I’ve witnessed this myself, when a patient has a very large, perhaps even an ulcerated tumour, yet metastases do not yet exist or only develop later.

N = lymph nodes

The condition of regional lymph nodes is designated by the letter N (nodulus in Latin). The degree of this letter indicates if cancer cells have been discovered in the lymph nodes and if they have, then where and how many.

N0 indicates that samples of the lymph nodes examined under the microscope revealed no metastasis. Here, it’s important how many lymph nodes have been examined. If only a few have been examined, then the N0 designation isn’t as convincing. This does not apply to examinations of the so-called sentinel lymph nodes (see earlier blogposts). If cancer cells are not found in the sentinel lymph nodes, then a designation of N0 is recorded, even if regional metastases have not been surgically removed. This designation encourages us to believe that the tumour has not yet spread further and therefore it’s possible that additional systemic therapy won’t be prescribed, especially if the tumour’s other indicators lead us to believe that the disease is less aggressive. On the other hand, the larger the number next to the letter N, the more severe the prognosis. Nx means that the lymph nodes cannot be evaluated. They have either not been removed or were removed earlier but no data regarding the operation remains. N1 usually indicates metastases in the closest lymph nodes or in a small number of lymph nodes. N2 and N3 indicate more widespread metastases in the regional lymph nodes and this interpretation can differ depending on the type of tumour.

M = metastases

This letter is also derived from the Latin (metastasis) and indicates metastases in other organs. M0 indicates that there are no other metastases in other locations. Doctors don’t usually look for metastases in other organs in patients with early diagnoses, especially if they don’t seem to have any complaints. M1 indicates that distal metastases have been found, even if this hasn’t been confirmed in the laboratory, but can readily be seen in PET or CT scans. Some tumours are broken down into even more complicated classifications, because some distant metastases can also differ. The Mx designation has since been removed from the TNM Classification, but it can be applied to cases where distal metastases can’t be diagnosed if, for example, the patient is in such a severe state that additional examinations could be dangerous.

One of the methods used to more precisely define the spread of the disease is a positron-emission tomography or PET/CT scan, and this is especially useful for patients with cancerous haematological            tumours, melanomas, lung tumours and digestive tract or gynaecological tumours. In this way, it’s possible to discover even small instances of metastases, even when there has been no suspicion of their existence. This, in turn, would change the treatment strategy as these differ for early-stage and metastatic tumours.

M1 indicates the beginnings of Stage IV. This, however, doesn’t mean that the patient can no longer be helped. There are still many ways to improve well-being, reduce tumour size and perhaps even hamper the further progression of the disease. This doesn’t necessarily mean the use of expensive drugs, which are often offered. In desperation, people are willing to try anything, even if it won’t help them.

By collecting these data – the size of the tumour, the condition of the lymph nodes and the progression of distal metastases – we can designate the stage of the disease. Usually when mentioning a diagnosis both the stage and the TNM designation are indicated to more precisely define how far the disease has spread. The TNM Classification doesn’t change over the course of the illness, because it only applies to the original tumour. If two tumours are discovered simultaneously or in each of a pair of organs (for example, the breasts), then each tumour is given its own TNM. The TNM can change after an operation. For example, prior to an operation a doctor may discover enlarged lymph nodes and describe them as N1, but later, after a sample is examined under a microscope and no metastases are discovered, the TNM is changed to N0. After the operation, the amended TNM is written as pTNM, where p denotes a pathologically verified diagnosis.


The prefix before the stage or TNM indicates how this information about the progress of the tumour was obtained. For example:


  • c means that the progress of the tumour was evaluated before treatment was administered and is based on clinical, laboratory, imaging or morphological test results;
  • p means that the tumour stage was evaluated by the histopathologic examination of a surgical specimen;
  • y means that the stage was assessed after neoadjuvant therapy (chemotherapy, radiation);
  • r means a stage for a patient who had no signs of cancer for a period of time, but who now is experiencing a recurrence;
  • a means that the stage was determined at autopsy.

There are still other tumours where other classification systems (FIGO, Dukes) are traditionally used to add still more information to the TNM. At the moment, a number of other indicators are also used with certain tumours (a Gleason score for prostate cancer,  Breslow’s depth for melanoma or a Bloom-Richardson grade for breast cancer). In any case, the TNM holds significant information about your tumour, so be sure to keep it in a safe place.

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