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Drugs of interest to pathologists

Drugs related to surgical pathology

Resin-based Yttrium 90-labeled microspheres

Author: Him G. Kwee, M.D. (see Reviewers/Authors page)
Revised: 8 November 2011, last major update November 2011
Copyright: (c) 2011, PathologyOutlines.com, Inc.


● Resin-based microspheres impregnated with the radionuclide Yttrium-90 for selective internal radiation therapy (SIRT)

Trade name

● SIR-Spheres

Clinical features

● Approved by US Food and Drug Administration in 2002 for unresectable hepatic metastases of colorectal carcinoma
● The incidence of adverse effects ranges from 0% to 13% and occurs within the first two months after the SIRT procedure
● The most frequent adverse reaction is gastric or duodenal inflammation with ulceration, which can cause bleeding and perforation; treat with proton pump inhibitors, avoid capecitabine (antineoplastic drug that may make symptoms worse)
● Other less frequent adverse reactions include pancreatitis, cholecystitis, hepatic failure, esophagitis and radiation induced pneumonitis (Arch Pathol Lab Med 2008;132:1734)
● The liver biopsy in hepatic failure shows non-specific changes such as microvesicular steatosis and swelling of hepatocytes, but the clue is the finding of the microsphere particles; particles also seen in gallbladders removed because of radiation induced cholecystitis (Radiographics 2005;25 Suppl 1:S41)
● Cost: approximately $14,000 in 2007 for one treatment (Issues in Emergent Health Technologies;102:2007)

Use for pathologists

● The Yttrium 90-microspheres are administered via hepatic artery branches to selectively deliver internal radiation therapy (SIRT) to inoperable liver metastases of colorectal carcinoma
● Microspheres are not metabolized and are not excreted and will remain permanently in the liver
● This therapy can cause extrahepatic adverse effects if the microspheres are incorrectly delivered in arteries supplying the stomach, duodenum or pancreas, as well as other organs
● Yttrium 90 is a pure beta emitter with a maximum penetration of 11 mm
● Its physical half life is about 64 hours and continual radiation emission lasts for about 14 days after the administration
● The histologic changes in the stomach and duodenum include apoptosis, epithelial flattening, ulceration with fibrinopurulent exudate, glandular cystic dilatation, mucin depletion, foveolar hyperplasia, epithelial atypia, capillary ectasia with prominent plump endothelial cells and granulation tissue formation with reactive stromal cells that may appear atypical
● Eosinophils may be numerous in the lamina propria
● On H&E, are distinct purple foreign particles measuring 40 micrometers, which are the microspheres; they are well formed and have a lighter peripheral halo; they resemble psammoma bodies, but they do not show concentric lamellation
● Microspheres can elicit a foreign body reaction
● Atypical epithelial and stromal cells in the biopsies should not be mistaken for malignancy
● Diagnosis should be made based on gastric or duodenal biopsy due to the microspheres, as the clinical symptoms and endoscopic appearance are non-specific

Differential diagnosis of Yttrium microspheres

Schistosoma japonicum: egg shells are larger (at least 70 micrometer), are more ovoid and have small spines
● Vegetable particles (pulse granuloma)
● Sodium polysterene sulfonate crystals (Kayexalate): Kayexalate crystals are not uniform in size and shape; mostly polygonal and measure up to 60 micrometers (Diagn Pathol 2008;3:27)

End of Drugs > Drugs related to surgical pathology > Resin-based Yttrium 90- labeled microspheres

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