Tumours that metastasise to bone may be remembered using the mnemonic "lead kettle" spelled PBKTL (lead is Pb on the Periodic Table).
- 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 metastasising to bone. The other 20% of primary disease sites in both sexes are: kidney, thyroid, gastrointestinal tract and other locations.
Lytic vs blastic in the "lead kettle" PB-KTL mnemonic
By knowing the typical behaviour of the metastatic lesion - lytic or blastic - you can help sort between the types to make the mnemonic even more useful.
- prostate = blastic/sclerotic (induces bone growth)
- breast = mixed pattern
- kidney, thyroid, lung = lytic (induces bone destruction)
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 "tumour-catching" places: liver, lung, peritoneum and others.
Carcinoma metastases are the most common malignant tumours 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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