Metastatic Bone Lesions

Incidence

• The most common bone carcinoma in elderly
• Usually 50 – 70 years old
• Bone is a common site for metastases, after lung and liver
• 60% of cancer patients have osseous metastasis
• 80% of the cancers involve bone
  • Breast and Prostate consist 2/3 of secondary deposit cases (breast alone 50%)
  • Lung, Thyroid, Kidney, Genitalia, Bladder, GIT consist 1/6 of cases
  • In remaining 1/6, primary site is not found
• Less than 0.1% of tumour cells entering the circulation survive, with resultant seeding and division

Clinically

• Deposits usually occur where red marrow is plentiful
  • Skull
  • Vertebrae (The most common site)
  • Pelvis
  • Ribs 
  • Upper ends of humerus and femur
• Symptoms and signs depend on the primary site
• May present with bone ache or pathological fracture
• Hypercalcaemia often associated with secondary deposits in bone manifesting with nausea, vomiting, anorexia, lethargy, confusion , stupor and eventually coma
• Increased calcium is secondary to bone resorption or humoral effects of secretions produced by the tumour

X-Rays

• Osteolytic deposits
  • Commonest 
  • Cortical destruction with little or no periosteal reaction
• Osteoblastic deposits
  • May occur occasionally in breast and bowel secondaries
  • Most commonly due to prostatic disease with mottled increase in density of the pelvis
  • Lymphoma deposits may resemble prostatic deposits
• Distal limb lesions (distal to elbow and knee) usually are lung or kidney metastases

Investigations

• Complete physical exam, esp. breast, thyroid, pelvic and DRE
• Bloods
• Calcium, Phosphorus, ALP, LFT, PSA, SPEP
• Urine tests and fecal occult blood
• X-Rays
• Chest and abdomen CT
• Bone scan
• May need biopsy of the lesion in unidentified cases

Pathology

• Microscopic lung seeding always evident where there are bone secondaries
• Division of cell progresses to invasion of capillaries and spread of tumour cells into peripheral circulation
• Spread to bone :
  • Hematogenous : 
    • Predilection for bone rather than other tissue such as muscle, due to character of red marrow
    • Bone receives 5 – 10% of cardiac output and the frequency of metastasis is greater than expected on a circulatory basis
  • Direct contiguous spread (rare)
  • Venous channels : Pelvic and breast metastases can reach vertebrae, as blood can be shunted into bone without passing through the liver and lungs

Treatment

• Solitary secondary may be amenable to surgery, esp. for hypernephroma and renal tumours
• Symptomatic treatment
• Drug therapy, radiotherapy and surgery may be used as palliative measures
• Hormone therapy in breast and prostatic disease may prolong survival
• Fractures should be stabilised if expected to live greater than one month 
• May use PMMA to augment fixation if expected survival is less than 1 year

Prognosis

• Survival after pathological fracture varies with the primary site
• Lung and kidney patients rarely survive more than 1 year
• Thyroid,prostate and breast patients usually survive more than 1 year
• Overall 50% survive for 6 months and 30% for 12 months