Immunoscintigraphy of colorectal cancer using 111In-labeled monoclonal antibody to mucin

Effect of radioimmunoscintigraphy on the management of recurrent colorectal cancer

BACKGROUND

Radioimmunoscintigraphy (RIS) is being used increasingly as a new investigation in the diagnosis of recurrent colorectal cancer. This study assessed the efficacy of 99mTc-radiolabelled PR1A3 scanning in a cohort of patients with possible recurrent colorectal cancer and the effects of scan interpretation on subsequent clinical management.

METHODS

The scans and case notes of patients scanned over a 3-year period were reviewed.

RESULTS

Forty-seven scans in 40 patients were available for analysis. In 39 instances in which scan interpretation could be verified accurately, sensitivity for recurrent colorectal cancer was 22 of 23 (96 per cent), specificity for recurrent colorectal cancer was eight of 16 (50 per cent), positive predictive value for recurrence was 22 of 30 (73 per cent) and negative predictive value for recurrence was eight of nine (89 per cent). In 16 of the 40 patients, scan interpretation strengthened a management decision or altered management. This was beneficial to ten patients and possibly detrimental to six.

CONCLUSION

This study demonstrated that RIS is sensitive in the detection of recurrent colorectal cancer and benefited the patient in one-quarter of cases. For the majority of patients, accurate detection of recurrent disease cannot be followed by curative therapy, but there is an important subgroup of patients in whom RIS alters management beneficially. However, a randomized prospective study is needed to confirm this.

Anti-murine antibody response to mouse monoclonal antibodies in cancer patients

Although development of human anti-murine immunoglobulin antibody (HAMA) is often seen in patients receiving murine antibodies, the variety of methods used for detecting HAMA makes it difficult to compare directly the HAMA responses measured by different assays. In the present study, several parameters of the HAMA response to two murine monoclonal antibodies were evaluated. The anti-sialosyl Tn antibody MLS102 and anti-CA125 antibody 145-9, which were labeled with 111In, were injected intravenously into 17 colorectal cancer patients and 11 ovarian cancer patients for immunoscintigraphy, respectively. HAMA was measured by enzyme-linked immunosorbent assay. There was no difference in baseline HAMA levels before antibody injection between the two groups. HAMA developed more frequently in ovarian cancer patients receiving the 145-9 antibody than in colorectal cancer patients receiving the MLS102 antibody (9/11 vs. 6/17, P < 0.05). No significant difference was observed in maximal HAMA levels between the two groups of patients. However, time to reach the maximal levels was delayed and the duration of the response seemed longer in ovarian cancer patients. Among 11 patients receiving the 145-9 antibody three patients became positive for HAMA more than 2 months after antibody injection and the other two had HAMA activity in their sera for more than 17 months. HAMA response was different between the two antibodies, and late onset or long duration of HAMA response against the 145-9 antibody suggests the importance of HAMA measurement in patients who receive a second injection of murine antibodies even after a long interval.

Effect of circulating antigen on immunoscintigraphy of ovarian cancer patients using anti-CA125 monoclonal antibody

The murine monoclonal antibody (mAb) 145-9 recognizes an epitope present on CA125 but different from the epitope defined by the mAb OC125. To evaluate the clinical usefulness of the 145-9 antibody, immunoscintigraphy was performed in ovarian cancer patients and the effect of circulating CA125 on tumor imaging was investigated. Two milligrams (74 MBq) of 111In-labeled 145-9 was injected intravenously into 11 patients with ovarian cancer. Pre-injection serum CA125 concentrations were between 166 U/ml and 7414 U/ml. Tumors were visualized in 10 of 11 patients. In two patients, lymph nodes that were not detected by other imaging modalities but were clinically suspected as metastases were visualized. There was no correlation between serum CA125 level and antibody uptake in the tumors. Immune complexes between the antibody and circulating antigen were observed in sera of all the patients, but the fraction of radioactivity in complex form did not correlate well with serum CA125 levels. The immune complexes survived in the circulation and the circulating radiolabel, including immune complexes, was still bound to solid-phase CA125. The plasma clearance rate and hepatic uptake of the antibody were not significantly affected by circulating CA125. In conclusion, the antibody 145-9 formed complexes with CA125 in vivo but this did not Compromise the outcome of antibody imaging. The antibody 145-9 can be used in immunoscintigraphy of ovarian cancer irrespective of serum CA125 level.