Small tumours – big impact

In oncology, a “small” tumour generally refers to a mass that is 2cm or less in diameter. Tumours under 1 cm are often described as “very small”. These small growths typically fall into the earliest clinical staging categories (such as T1) where they are highly localized and have not spread beyond nearby structures. Tumor Size Comparison – to conceptualize these measurements, oncologists often use common food items as visual benchmarks:

1 mm to 5 mm: A grain of rice or sprinkle.
1 cm (10 mm): A standard pea or coffee bean.
2 cm (20 mm): A peanut or large marble.

Importance of Size in Tumour Staging

While a smaller size generally indicates an early-stage cancer with a better prognosis, the true clinical significance depends heavily on cancer type, cellular aggressiveness (grade), and lymph node involvement. For example, in breast cancer, early stage (Stage 1A) is specifically classified as 2 cm or smaller. Conversely, for bladder cancer, small tumours are typically defined as 3 cm or less. Size within staging definitions is defined by the T (the T in an acronym known as TNM) and in particular the breakdown showing approximate sizes and criteria, e.g. T1, T2, T3, T4. In some cancers, T1 (and stage) is further divided e.g. T1a, T1b etc.

So what about NET? One of the key differences you will find in NET is the difference in staging definitions for different primary types – i.e. they are a heterogenous collection of tumours. For example You can read about Staging for Neuroendocrine Neoplasms by clicking here. You will see the various size definitions for each under T1 definitions. For example:

Appendiceal NETs – T1 – less than or equal to 2cm
Small Intestine NETs – T1 – less than or equal to 1cm
Pancreatic NETs – T1 – less than or equal to 2cm
Gastric NETs – T1 less than or equal to 1cm
Lung NETs – T1 – more complicated so they are broken down into T1a, T1b, T1c etc – all different sizes.

Stage IV

Cancer is defined entirely by the spread of cancer to distant parts of the body, meaning the primary tumour can actually be very small, or even undetectable. As above, in oncology, staging relies on the TNM system (Tumour size, Node involvement, distant Metastasis). If “M” is confirmed as distant metastasis, the cancer is automatically categorized as Stage IV—even if the “T” category is at its lowest numeric value. If you wanted to know more about staging definitions, see my staging blog linked above. Some NETs, as you can see above, have small tumours but still frequently present as Stage IV. They are notorious for often growing at an exceptionally slow rate and even though they can grow without clinical detection for many years before found, a small primary NET can remain small—often well under 2 cm – and yet aggressively shed cells that can migrate to the liver and other places. In many NETs, particularly small intestine and pancreas (and others), it’s common for patients to have large, symptomatic liver metastases while the original primary tumour remains tiny.

All of the above presents diagnostic difficulties for clinicians and beyond that makes surveillance and treatment of these tumours highly complex. We need more research, more awareness, better markers. Now that NETs are mainstream, this area should improve but it won’t be overnight. One key challenge is classification table are mostly driven by anatomy not cell based, unintentionally masking NET from the attention it desperately needs. The sooner the NET scientific and the international classification communities can resolve this unfair anomaly, the better.

You can help by understanding how to reframe NET beyond rare.