6.6. METASTATIC BONE PAIN
461
6.6. PALLIATIVE TREATMENT OF METASTATIC BONE PAIN
6.6.1. Clinical benefits
The aim of radionuclide therapy for metastatic bone pain is to ameliorate
pain, reduce the intake of analgesics and improve quality of life. The
requirement for such treatment is the demonstration of good focal uptake of
99m
Tc bone-seeking radiopharmaceuticals in bone scintigraphy at sites corre-
sponding to the bone pain. The main primary tumours are carcinomas of the
prostate, breast and lungs. Similar results have been obtained using
32
P (as the
orthophosphate),
89
Sr (as the chloride) and
153
Sm (as ethylene-diamine-tetra-
methylene-phosphonate (EDTMP)). Between 60 and 75% of patients
normally show a good response to such treatments; the duration of response
lasts between 6 and 24 weeks (with a mean of 12 weeks) and is independent of
the radioisotope used. A significant proportion (40–50%) of responders do not
require analgesics, while the rest require only mild doses of oral analgesics in
order to remain free of pain. Studies have also demonstrated that there is
significantly delayed onset of new bone pain following therapy.
Mild to moderate myelosuppression (thrombocytopenia, leucopoenia
and rarely anaemia) is sometimes observed. Haematological toxicity with
32
P
may be minimally greater than that with
89
Sr or
153
Sm-EDTMP, but rescue
strategies are rarely required.
6.6.2. Physiological basis
Bone metastases have local effects resulting in increased bone
destruction (osteolysis), increased bone formation (osteosclerosis) or both.
Osteolytic metastases are the predominant types of lesions in most cancers, but
a sclerotic appearance is seen in the majority of metastases from prostate
cancer, in about 10% of metastases from breast cancer, as well as in those from
other cancers. In the majority of skeletal metastases, new bone formation
develops simultaneously with bone destruction, and the radiological
appearance reflects the process that predominates.
Bone seeking, beta emitting radiopharmaceuticals such as
32
P-orthophos-
phate,
89
Sr-chloride,
188
Re-HEDP and
153
Sm-EDTMP demonstrate a rapid
blood clearance with prompt localization in areas of bony repair. Systemic
administration provides a means of delivering radiation systemically to the sites
of disseminated bone metastases. Several other beta or conversion electron
emitting radiopharmaceuticals (
117m
Sn-DTPA and
166
Ho-(1,4,7,10-tetra-azacy-
clododecane-1,4,7,10-tetramethylene phosphonic acid) (DOTMP)) are also
being evaluated and have shown promise.