Tumors that metastasize to bone (mnemonic)

Last revised by Daniel J Bell on 11 Jun 2022

Tumors that metastasize to bone may be remembered using the mnemonic "PBKTL", rendered as "lead kettle", as "Pb" is the standard abbreviation for the chemical element, lead.

  • PB-KTL

  • P: prostate
  • B: breast
  • K: kidney
  • T: thyroid
  • L: lung

For females, breast and lung are the most common primary sites ; nearly 80% of cancers that spread to the skeleton are from these locations. In males, prostate and lung cancers make up 80% of carcinomas metastasizing to bone. The other 20% of primary disease sites in both sexes are: kidney, thyroid, gastrointestinal tract and other locations.

By knowing the typical behavior of the metastatic lesion - lytic or blastic - you can help sort between the types to make the mnemonic even more useful.

The spreading pathways of metastasis from the starting site to the bones are only partially understood, and some authors propose some bone metastasis via the Batson venous plexus, a two-way, valveless venous pathway that allows cancer cells, infection and emboli to travel freely both to cranial and caudal direction without passing through the main "tumor-catching" places: liver, lung, peritoneum and others.

Carcinoma metastases are the most common malignant tumors in the skeleton, with maybe somewhat vague symptoms or an acute onset, often with pain or pathological fractures. In people with breast and prostate cancer, the bone is often the first distant site of cancer spread. More than 2 out of 3 breast and prostate cancers that spread to other parts of the body spread to the bones. Of lung, thyroid, and kidney cancers that spread to other parts of the body, about 1 out of 3 will spread to the bones.

Basic knowledge of a simple mnemonic about the main types of bone metastases can be a handy tip in the medical routine: with a good history taking from the patient, clinical findings and sharp eyes on the images it is possible to nail a nice and elegant diagnostic hypothesis allowing a more specific investigation.

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