Leukaemic sanctuaries

Chris Dwyer suggested that I expand a little about sanctuaries so

Malignant cells, by definition, are very capable of moving into and living in tissues to which they have little to no relationship. That is called metastasis. You may have noticed that some malignancies seem to "prefer" certain locations and other malignancies end in different places.

Early in development, the embryo starts cell differentiation by developing 3 different types of tissue. They are called (from inside out) endoderm, mesoderm, and ectoderm. Ectodermal tissue forms the whole of the nervous system, the epidermis of the skin, the lining cells of the sebaceous and mammary glands, the hairs and nails, the epithelium of the nose and adjacent air sinuses, and that of the cheeks and roof of the mouth. From it also are derived the enamel of the teeth, and part of the lower brain the epithelium of the cornea, conjunctiva, and lacrimal glands, and the part of the sense organs.

Endodermal (or entodermal) tissue forms the lining of the whole of the digestive tube excepting part of the mouth and pharynx and the terminal part of the rectum, the lining cells of all the glands which open into the digestive tube, including those of the liver and pancreas, the epithelium of the auditory tube and tympanic cavity, of the trachea, bronchi, and air cells of the lungs, of the urinary bladder and part of the urethra, and that which lines the follicles of the thyroid gland and thymus.

Almost everything else that is not mentioned all come from mesodermal tissue.

It is believed that metastasis is more 'successful' if the malignant cell ends up in a place that arose from the same primitive tissue. So, colon cancer ends up in the bone because they both arose from the same primitive cells. Similarly, breast cancer seems to like metastasizing to the brain.

But that is different from sanctuaries. A sanctuary is a place whose lining cells protect that area from insult from the outside. If these lining cells are working properly, these are places which are not even recognized by the immune system as self . They include the brain, testes, thyroid, eye, and part of the pancreas. In the brain,for example, these lining cells permit only a very small number of compounds - like glucose - to be transferred from the plasma into the tissue. So, if there is a malignant cell or two in there, giving chemo via its normal route - by mouth or iv - isn't going to work. Radiation can get through because ions don't care about cell membranes. But chemo can only get to these tissues if it is put their directly. In the case of the central nervous system (brain and spinal cord), this means that the medication must be put directly into the cavity that houses the spinal cord (intrathecal administration) in the process similar to getting a spinal anesthetic.

This is the reason that many times you end up having to have a spinal tap - to determine if there are any cells in there and if there are - how many.