Imaging of medullary carcinoma of the thyroid using 111In-labelled anti-CEA monoclonal antibody fragments

The Use of Monoclonal Antibodies for Radioscintigraphic Detection of Cancer

Beginning with Ehrlich's original “magic bullet” concept of 1904, the pioneering human trials in the late 1970s of Goldenberg and Mach using polyclonal antibodies, and the Nobel Prize-winning work of Kohler and Milstein in 1975 for developing monoclonal antibody (MAb) technology, there has been much interest in the use of antibodies for detecting and treating cancer. Although not the revolutionary breakthrough that was initially hoped for, marked progress has been made. The Food and Drug Administration (FDA) has recently approved the intact murine IgG, 111-indium CYT-103 (satumomoab, Oncoscint™ Cytogen, Princeton, NJ) for clinical use in detecting colorectal and ovarian cancer. However, the agent has been approved for only a single, one-time use, because patients developed an immune response (human anti-mouse antibody, or HAMA) that alters MAb biodistribution and may limit the clinical effectiveness of this agent when repeat studies are performed. Other MAbs reacting with a variety of antigens and targeting numerous tumors, including breast, lung, prostate, and melanomas, are currently undergoing large-scale clinical trials. To reduce induction of immune responses, many of the agents use immunoglobulin fragments [Fab, or F(ab)2] labeled with the short-lived isotope 99m-technetium used for most routine nuclear medicine diagnostic testing. Future developments will use even smaller fragments such as single chain antibodies or custom synthesized molecular recognition units (small peptides containing only the specific antigen combining site). Presented herein is an overview of the past results and an assessment of the current status of radioimmunoscintigraphy for various neoplasms.

Pretargeted immunoscintigraphy in patients with medullary thyroid carcinoma

To evaluate the use of pretargeted immunoscintigraphy (ISG) in the diagnosis and follow-up of patients with medullary thyroid carcinoma (MTC), we studied 25 patients with histologically proven disease; ISG was repeated after surgery in two patients. The antibody, either an anticarcinoembryonic antigen (CEA) or an antichromogranin A (CgA) biotinylated monoclonal antibody (MAb) or a cocktail of the two biotinylated MAbs was first injected. After 24 h, avidin was administrated i.v., followed by 111In-labelled biotin 24 h later. Fifty-two lesions were visualised. Six primary tumours, diagnosed by increased calcitonin levels, were all correctly diagnosed; 47 recurrences, also suspected by blood tumour markers, were detected and confirmed by cytology or histology. In one case, single photon emission tomography allowed the detection of small lymph nodes with a diameter of 4-7 mm. These lesions, not judged neoplastic by ultrasound, were confirmed to be neoplastic by fine needle aspiration. Pretargeted ISG correctly localises primary tumours and recurrences in MTC patients, when the only marker of relapse is serum elevation of calcitonin. With this three-step pretargeting method, cocktails of potentially useful MAbs can be used, avoiding false-negative studies that may occur when CEA or CgA are not expressed.

Combined use of 111In-DTPA-D-Phe-1-octreotide (OCT) and 123I-vasoactive intestinal peptide (VIP) in the localization diagnosis of medullary thyroid carcinoma (MTC)

Although serum calcitonin and CEA are sensitive indicators for the presence of medullary thyroid carcinoma (MTC), the localization of tumor sites may be very difficult. In an approach to localize MTC lesions we performed comparative in vivo studies in 12 patients with primary MTC and in 4 patients with suspected recurrent MTC using 123I-VIP (150 MBq/1 microgram) and 111In-DTPA-D-Phe-1-octreotide (111In-OCT; 150 MBq/1 microgram). Despite elevated calcitonin values in all patients with suspected recurrent or metastatic lesions, both ultrasound and computed tomography (CT) were unable to localize a tumor site. 111In-OCT localized the primary tumor in the thyroid gland in 7 of 11 patients (63.5%). In 2 of 4 patients (50%) with suspected recurrent MTC, pathological uptake of 111In-OCT in the mediastinum or liver was demonstrable. In none of the 11 patients did 123I-VIP-receptor scanning indicate primary, recurrent, or metastatic tumor lesions. In vitro binding studies showed an absence of high-affinity VIP receptors in MTC tissue, whereas high-affinity 111In-OCT receptors were present in 4 of 6, and low-affinity 123I-VIP as well as 111In-OCT receptors were present in 6 of 6 MTC tissue samples. We conclude that somatostatin receptor scanning using 111In-OCT may visualize primary MTC, but it has only a low sensitivity in the detection of recurrent disease. The 123I-VIP-receptor scan is not helpful in the localization diagnosis of primary or recurrent MTC.

Imaging in thyroid cancer

No ideal imaging method is available for the diagnosis of MTC. Once the diagnosis is suspected, serum calcitonin or CEA may help to confirm it. Often, multiple studies are done, especially a combination of MR imaging or ultrasound and an isotopic method. Tc(V)DMSA is an excellent agent but not readily available in the United States. Indium-labeled pentreotide is probably the imaging agent of choice in the United States.

[Immunoscintigraphy in oncology]

In vivo immunotargeting of specific antigens with radiolabeled monoclonal antibodies is a new method of diagnosis which has largely improved over the past 15 years. It has been especially developed in the oncologic field. Although it is not yet a daily procedure, immunoscintigraphy has been proven a useful diagnostic tool in many situations. It gives information about the presence of lesions and their neoplastic nature. For this reason, immunoscintigraphy appears as very complementary to morphological imaging and is mainly indicated when lesions have insufficient anatomical definition. Early detection of recurrences is actually the best indication of immunoscintigraphy. However, some problems still exist, concerning the tumor/tissues uptake ratio which is not sufficient for an optimal imaging contrast, and the apparition of human anti-mouse antibodies (HAMA) in the patients. At present, many works are in progress which could resolve these problems. Ultimately, well-performed clinical trials are necessary to establish the right place for immunoscintigraphy in the diagnostic and therapeutic strategies in oncology.

Detection of cervical metastases of thyroid medullary carcinoma by MoAb anti-CEA scintigraphy and immunohistochemistry

Four patients with medullary thyroid carcinoma (MTC) were examined using anti-carcinoembryonic antigen (CEA) scintigraphy. Two patients had positive and two normal scintigraphic findings, although all the patients had elevated blood test markers (calcitonin or CEA). One patient with clinical suspicion of MTC metastases had only a faintly positive anti-CEA image, although single-photon emission tomographic scanning was used to increase the sensitivity and resolution of the method. Therefore, digital image processing of the planar images was performed to obtain more detailed information. The analysis revealed distinct accumulation of the activity at the right side of the neck at 20 h post administration. The specificity of the antibody binding in the malignant cells was confirmed after surgery by immunohistochemical staining of the tumour specimens for CEA. Both conventional and confocal laser scanning microscopy revealed distinct positive staining, indicating that the results obtained from the anti-CEA scanning showed specific binding of the labelled antibody in the neoplastic tissue.

Radioimmunodetection of malignant solid tumours

An increased clinical utility of radiolabelled monoclonal antibodies (MoAb), recognizing a variety of different antigens expressed preferentially in malignant tissue, for localizing primary, metastatic and recurrent cancer has been documented in many recent investigations. This review focuses on both basic and practical aspects of radioimmunodetection in oncology and is a status report on the performance and limitations of radiolabelled antibody procedures currently applied to the clinical detection of malignant solid tumours. At this time clinically validated radioimmunodetection methods are available for colorectal, ovarian, breast, lung, thyroid medullary, and head and neck carcinoma, and melanoma. Recent advances in humanization of MoAb significantly improve the prospects of effective antibody-guided radiotherapy in the near future.

The role of functional imaging in neoplasms of the thyroid

Iodine-123 and Iodine-131 have suitable physical properties that enable them to be used for functional imaging of the thyroid. Iodine-123 is used for routine testing for hyperthyroidism and thyroid nodules, whereas I-131, which has a longer half-life, is used for whole body imaging for detecting metastatic thyroid cancer in patients who have undergone thyroidectomy. The radionuclides of iodine are trapped and organified like nonradioactive iodine. In contrast, technetium as pertechnetate is trapped by the thyroid and can be used for imaging immediately after intravenous injection. There can be differences in scintiscans made in the same patient using radioiodine vs. technetium. Thallium is a useful adjuvant imaging agent for thyroid cancer. It should be stressed that correlation with the clinical findings and biochemical thyroid function tests are very important when evaluating thyroid scintiscans.