H-15 (HT-29-15) is an
IgG1 mouse
monoclonal antibody (mAb) to a
cell surface antigen (molecular mass, 200,000 daltons) present on virtually all
colorectal cancers and also in normal pancreatic ducts and bile ducts, but not in other normal tissues. The
biological distribution and imaging characteristics of
iodine-131 (131I)-labeled mAb H-15 were studied in 5 primary
colorectal cancer patients and 9 patients with local recurrence of
colorectal cancer. H-15 mAb labeled with 0.5-10 mCi of 131I was administered 7 to 8 days before surgery at 4 dose levels, ranging from 0.2 to 6 mg. Selective mAb H-15 localization to
tumor tissues was demonstrated in 6 of 12 patients with
antigen-positive
tumors: in two patients, recurrent
tumors were negative to H-15 mAb, although the primary
tumors were positive. In six patients with positive radioimaging,
tumor:normal tissue ratios ranged from 2.05 to 5.35 and
tumor:serum ratios from 1.18 to 2.73. The clarity of images seems to correlate well with the latter ratios.
Technetium-99 (99mTc)-albumin blood pool studies in selected cases showed that local recurrence of
colorectal cancers was hypovascular, emphasizing the selective localization of mAb H-15 despite poor blood flow distribution in the
tumors. The results altogether demonstrated that radioimmunodetection with 131I mAb H-15 is valuable for differentiating recurrent
colorectal cancer from
granuloma formation after surgery.