Acid Reflux -> Oesophagitis -> Barrett's Oesophagus -> Oesophageal cancer
Acid refluxing into the oesophagus may wash aside the mucous lining and attack the squamous cells beneath - in the same way as pouring acid on your hand would burn and scar. This may be felt as heartburn and continued erosion can result in oesophagitis.
If bile refluxes onto the inflamed area, it could permit the acid to start digesting the exposed lining in the same way as it would break down ingested animal products. As a protection, the squamous cells can be replaced by columnar cells.
An analogy is to think of squamous cells as dominoes lying on a table. Columnar cells are like dominoes standing on end with a smaller surface exposed to attack. Meanwhile the nerves centred within the cells are further moved from the attack so these cells are effectively less sensitive and the misery of heartburn may diminish. These cells resemble those that line the stomach or intestines and may be described as gastric or intestinal metaplasia.(There is some discussion as to whether Barrett's cells are actually "metaplasia", which infers they are changed squamous cells or whether they are actually new cells produced from stem cells - as discussed in a July 2017 paper "Barrett’s Stem Cells as a Unique and Targetable Entity" [c-i])
This is the condition known as Barrett's Oesophagus and it is a permanent change. Sometimes Barrett's appears to go away but if it's not seen, it may be hidden in the corrugations of the epithelium or a second mucosal layer may have grown over it. The burning sensations may reduce or disappear adding to the illusion that the Barrett's has gone but Barrett's itself is asymptomatic and the cells being less sensitive are protecting against the pain.
However, these cells are unregulated and in a small minority of cases can mutate. In our analogy, it's like some of the dominoes toppling. This is called Low Grade Dysplasia (LGD).
If a large mass of these dominoes topples into a disorganised heap, it's known as High Grade Dysplasia (HGD).
Further mutations may now occur which can cause a proliferation of mutated cells which is Oesophageal Adenocarcinoma - that's cancer!
The different stages of Barrett's Oesophagus are:
1. Non-Dysplastic Barrett's Oesophagus (NDBO/NDBE)
2. Low Grade Dysplasia (LGD)
3. High Grade Dysplasia (HGD)
4. Neoplasia - initial stage of adenocarcinoma. (OAC/EAC)
The phrase "Indefinite for Dysplasia" is often used if there is uncertainty whether it's NDBO or LGD.
It must be stressed that the chances of progression of Barrett's Oesophagus to Oesophageal cancer are very low and it is treatable.
(Just under 8000 people die each year from Oesophageal Cancer out of 64 million in UK, making the chances one in 8000. If there are 3 million with non-dysplasic Barrett's*, their risk is one in 400.)
Britain tops the world for incidence of oesophageal cancer where it is the fifth greatest cancer killer of men, claiming the life of one person an hour on average in the UK. [c-ii]
If it is going to occur, the progression is usually slow initially but by the time cancerous cells develop, it's frequently too late to treat with life expectancy measured in weeks rather than years.
* A paper published in 2014 [c-iii] suggests one in 20 have Barrett's. Applying that to the UK population implies there may be 3 million people with Barrett's though fewer than 150,000 know it. If the others can be identified, it may be possible to prevent this large number of deaths.
The size and extent of an observed area of Barrett's may be described using the Prague criteria using the letters c for circumferential ring and m for maximum length of any tongues. Thus c2m3 would mean a ring of Barrett's 2 cm wide with protrusions to a maximum of 3 cm.
The next page describes in simple terms how Barrett's Oesophagus probably forms.