Introduction
Metastasis is a state of cancer where the cancerous cells invade a different part of the body to form secondary tumours. Due to the mobile nature and immortal nature, the cells are able to adapt to the new environment.
- The form their own microenvironment, providing their own vasculature and supply to survive and develop
- Cancer staging is given by TNM, or initial site of the tumour, if it has spread to nymph nodes, and where in the body it has spread.
Estimated cumulative lifetime of 0.1-0.25%
- Microscopic metastatic intraocular lesions estimated in at least 1 of 5 eyes to 10% people at time of death
- Eye tumours are not always detected until shortly before death when patient is already in palliation and terminal stages of cancer
- For the eye, dude to the vasculature of the choroid, it is the most common place for metastasis
Dead Giveaways
Anatomical-Mechanical Entrapment Theory
Proposed by Ewing 1928
Tumour cells follow circulation draining from the primary tumour, and are retained non-specifically in the capillary bed of the first organ encountered
So in the choroid, due to the short posterior arteries being the preferential route for embolic cells, a similar theory is applied for tumour cells
Due to the blood retinal barrier, secondary tumours are typically localised to the choroid.
Additionally, the short posterior arteries do not extend all the way to ciliary body or iris, which may explain why they are less affected as well.
Seed and Soil Theory
Proposed by Paget 1889
Depends on blood flow, and the choroid has one of the most vascular tissues in the body.
0.01% of cardiac outflow is directed to the eye, which is around 0.6-0.8 ml/min
But 80-85% goes to the choroid
The seed or the tumour is placed in an environment or soil that provides nutritional benefit to it, allowing for less drastic adaptation, and hence growing into a secondary tumour
diagnostic features
Origin of Metastasis
Realistically, can be from anywhere in the body
40-53% are from breast cancer
20-29% are from lung cancer
Non-specific Presentation
May not be the case for all metastasised tumours
Can be multifocal and bilateral in 1/4 cases
Usually <3mm thick with overlying RPE changes
Symptoms depends on SRF, location and size