Identification of calcitonin and calcitonin gene-related peptide messenger ribonucleic acid in medullary thyroid carcinomas by hybridization histochemistry

Expression of the Calcitonin Receptor-like Receptor (CALCRL) in Normal and Neoplastic Tissues

Little information is available concerning protein expression of the calcitonin receptor-like receptor (CALCRL) at the protein level. Here, we developed a rabbit monoclonal antibody, 8H9L8, which is directed against human CALCRL but cross-reacts with the rat and mouse forms of the receptor. We confirmed antibody specificity via Western blot analyses and immunocytochemistry using the CALCRL-expressing neuroendocrine tumour cell line BON-1 and a CALCRL-specific small interfering RNA (siRNA). We then used the antibody for immunohistochemical analyses of various formalin-fixed, paraffin-embedded specimens of normal and neoplastic tissues. In nearly all tissue specimens examined, CALCRL expression was detected in the capillary endothelium, smooth muscles of the arterioles and arteries, and immune cells. Analyses of normal human, rat, and mouse tissues revealed that CALCRL was primarily present in distinct cell populations in the cerebral cortex; pituitary; dorsal root ganglia; epithelia, muscles, and glands of the larger bronchi; intestinal mucosa (particularly in enteroendocrine cells); intestinal ganglia; exocrine and endocrine pancreas; arteries, capillaries, and glomerular capillary loops in the kidneys; the adrenals; Leydig cells in the testicles; and syncytiotrophoblasts in the placenta. In the neoplastic tissues, CALCRL was predominantly expressed in thyroid carcinomas, parathyroid adenomas, small-cell lung cancers, large-cell neuroendocrine carcinomas of the lung, pancreatic neuroendocrine neoplasms, renal clear-cell carcinomas, pheochromocytomas, lymphomas, and melanomas. In these tumours with strong expression of CALCRL, the receptor may represent a useful target structure for future therapies.

A Calcitonin Non-producing Neuroendocrine Tumor of the Thyroid Gland

Neuroendocrine tumors of the thyroid gland are generally considered to derive from parafollicular endocrine cells (C cells) and are generally referred to as medullary thyroid carcinomas (MTC). Calcitonin secretion is almost always detected in MTC and a prerequisite for both clinical and pathological diagnosis. Thyroid neuroendocrine tumors without any apparent calcitonin secretion reflect a diagnostic dilemma because non-calcitonin-producing MTCs have virtually not been characterized. Here, we report a case of primary thyroid neuroendocrine tumors lacking calcitonin secretion or expression. The tumor cells expressed cytokeratins, chromogranin A, and synaptophysin, all of which were consistent with epithelial and neuroendocrine differentiation. Thyroid transcription factor-1 paired box gene 8, and carcinoembryonic antigen were also immunohistochemically detected, consistent with its thyroid origin. However, the tumor was negative for calcitonin both by immunohistochemistry and in situ hybridization, hence, not meeting the definition of MTC. Despite the loss of calcitonin expression, immunoreactivity for the calcitonin-gene-related peptide was detected in the tumor. Somatic gene mutations of RET, H-RAS, K-RAS, or BRAF were not detected in this case. A limited number of calcitonin non-producing thyroid neuroendocrine tumors are available in the scientific literature available in English, and its etiology and clinical manifestations remain largely unknown. Our case, along with the rare, previously reported cases, suggests that calcitonin non-producing neuroendocrine tumors of the thyroid gland are most likely derived from C cells, but should be differentiated from ordinary MTCs.

Measurement of calcitonin and calcitonin gene-related peptide mRNA refines the management of patients with medullary thyroid cancer and may replace calcitonin-stimulation tests

BACKGROUND

Serum calcitonin (sCT) is the main tumor marker for medullary thyroid cancer (MTC), but it has certain limitations. Various sCT assays may have important intra-assay or interassay variation and may yield different and sometimes conflicting results. A pentagastrin- or calcium-stimulation calcitonin (CT) test may be desirable in some situations. Alternatively, or in the absence of the stimulation test, mRNA detection offers the advantages of being more comfortable and less invasive; it only requires blood collection and has no side effects. The objective of this study was to investigate the applicability of measuring calcitonin-related polypeptide alpha (CALCA) gene transcripts (CT-CALCA and calcitonin gene-related peptide [CGRP]-CALCA) in patients with MTC and in relatives diagnosed with a RET mutation and to test mRNA as an alternative diagnostic tool for the calcitonin-stimulation test.

METHODS

Twenty-three healthy controls and 26 individuals evaluated for MTC were selected, including patients with sporadic or hereditary MTC and RET mutation-carrying relatives. For molecular analysis, RNA was extracted from peripheral blood, followed by cDNA synthesis using 3.5 μg of total RNA. Quantitative real-time polymerase chain reaction (RT-qPCR) was performed with SYBR Green and 200 nM of each primer for the two specific mRNA targets (CT-CALCA or CGRP-CALCA) and normalized with the ribosomal protein S8 as the reference gene.

RESULTS

We detected CALCA transcripts in the blood samples and observed a positive correlation between them (r=0.946, p<0.0001). Both mRNAs also correlated with sCT (CT-CALCA, r=0.713, p<0.0001; CGRP-CALCA, r=0.714, p<0.0001). The relative expression of CT-CALCA and CGRP-CALCA presented higher clinical sensitivity (86.67 and 100, respectively), specificity (97.06 and 97.06), positive predictive value (92.86 and 93.75), and negative predictive value (94.29 and 100), than did sCT (73.33, 82.35, 64.71, and 87.50, respectively). In addition, the CALCA transcript measurement mirrored the response to the pentagastrin test.

CONCLUSION

We demonstrate that the measurement of CALCA gene transcripts in the bloodstream is feasible and may refine the management of patients with MTC and RET mutation-carrying relatives. We propose considering the application of this diagnostic tool as an alternative to the calcitonin-stimulation test.

Diagnosis of metastatic neoplasms: an immunohistochemical approach

CONTEXT

It is important to determine the type and/or site of origin of metastatic tumors for optimal clinical management.

OBJECTIVE

To summarize the use of currently available immunohistochemical markers in the evaluation of metastatic tumors.

DATA SOURCES

Review of relevant literature on immunohistochemical evaluation of tumors and the author's personal experience.

CONCLUSIONS

Immunohistochemistry is an important ancillary technique for evaluation of metastatic tumors and should be used in the context of routine morphology and clinical information. While a single marker may be used to support a known or suspected site of origin, a carefully constructed panel is strongly recommended, particularly for tumors of morphologically uncertain lineage or origin.

Application of immunohistochemistry to thyroid neoplasms

CONTEXT

Thyroid lesions with nodular architecture and follicular pattern of growth often pose difficulties in accurate diagnosis during the assessment of cytologic and histologic specimens. The diagnosis of follicular neoplasm on cytology or of follicular tumor of uncertain malignant potential on histology is likely to cause confusion among clinicians and delay effective management of these lesions. Occasionally, thyroid tumors represent unusual or metastatic lesions and their accurate diagnosis requires immunohistochemical confirmation.

OBJECTIVE

To review the literature on the applications of immunohistochemistry in the differential diagnosis of thyroid tumors.

DATA SOURCES

Relevant articles indexed in PubMed (National Library of Medicine) between 1976 and 2006.

CONCLUSIONS

Our review supports the use of ancillary techniques involving a panel of antibodies suitable for immunohistochemistry and molecular analysis in the assessment of thyroid nodules. These tools can improve diagnostic accuracy when combined with standard morphologic criteria.

Practical markers used in the diagnosis of endocrine tumors

Endocrine tumors constitute a large group of neoplasms that are widely dispersed throughout the body. They are made up mostly of neuroendocrine tumors (NE), which are characterized by the presence of secretory granules and production of peptide hormones, and non-NE tumors such as those derived from thyroid follicular cells and adrenal cortical cells. Immunohistochemical markers have been used to characterize these lesions and distinguish them from other histologically similar tumors. Chromogranin and synaptophysin are the most widely used broad-spectrum neuroendocrine tumor markers. The use of antibodies to transcription factors, keratins, and specific peptides is quite valuable in the diagnosis of endocrine tumors. This article reviews the common markers used to characterize endocrine tumors and to recognize tumors involved in the differential diagnosis of specific lesions.

Practical markers used in the diagnosis of neuroendocrine tumors

Although there are many broad-spectrum neuroendocrine markers, chromogranin and synaptophysin are the principal ones used in diagnostic pathology. Other broad-spectrum neuroendocrine markers, transcription factors, and specific peptide markers used in the diagnosis of neuroendocrine tumors are reviewed. The use of different keratins in the differential diagnosis of endocrine tumors is also presented. The importance of using low-molecular-weight keratins such as CAM5.2 to avoid false-negative results in the workup of some neuroendocrine tumors is emphasized. Finally, the use of in situ hybridization in diagnostic pathology is briefly summarized.

Polymerase chain reaction in the detection of tumor cells: new approaches in diagnosis and follow-up of patients with thyroid cancer

Thyroid cancers are the most common endocrine malignancies and are being diagnosed with increasing frequency. In addition to other measures, diagnosis is based on fine-needle aspiration cytology examination. Recently, new assays using reverse transcription-polymerase chain reaction (PCR) are being tested to improve sensitivity and specificity of primary diagnosis and detection of recurrent thyroid cancer. In the preoperative diagnosis of thyroid cancer, several tissue- and/or tumor-specific mRNA have been described and in several cases, a higher sensitivity and specificity could be achieved using molecular techniques compared to conventional methods. In the postoperative follow-up of patients with thyroid cancer, conflicting data have been published and the use of PCR techniques revealed several problems of the molecular approach, which are based on some technical as well as biologic limitations. Despite these problems, which are discussed in detail in this review, molecular techniques may nevertheless improve the sensitivity and accuracy of fine-needle aspiration of thyroid nodules, fine-needle aspiration of metastases, and detection of recurrent disease in peripheral blood samples.

Hybridocytochemical and immuno-ultrastructural study of calcitonin gene expression in cultured medullary carcinoma cells

The study was aimed at a morphological demonstration of calcitonin (CT) gene expression in cultured TT cells, or, more specifically, hybridocytochemical detection of CT mRNA and calcitonin gene-related peptide (CGRP) mRNA and ultrastructural localization of the two hormones. The TT cells originated from medullary carcinoma of human thyroid gland. Ultrastructural studies of TT cells demonstrated a well-developed rough endoplasmic reticulum, large Golgi apparatus and low number of secretory granules. Hybridocytochemical studies showed the presence of mRNAs for CT and CGRP in all TT cells. At the ultrastructural level, double immunolabelling demonstrated that the two hormones were always expressed together in the same secretory granules. Our results provide a significant addition to the biochemical studies performed up to now and indicate that all TT cells produce both mRNAs and both hormones in parallel.

CGRP radioreceptor assay: a new diagnostic tool for medullary thyroid carcinoma

The quantitative analysis of immunoreactive calcitonin (iCT) is the assay of choice for diagnosis and follow-up of patients with medullary thyroid carcinoma (MTC). However, in a small percentage of patients with MTC or C cell hyperplasia (CCH), basal and stimulated iCT levels may not be significantly elevated. In these patients, calcitonin gene-related peptide (CGRP) radioreceptor assay (RRA) can be used complementary to immunoassay for CT (or katacalcin) for prompt diagnosis of MTC and CCH. CGRP RRA is a robust, rapid, sensitive, and specific determinant of "receptor-recognized" CGRP (RR-CGRP; intact molecule of CGRP) either in plasma or in tissue extracts. Plasma RR-CGRP levels rose > 100% 2-5 minutes after stimulation with intravenous pentagastrin (calcium or oral alcohol) (p < 0.001), whereas iCGRP levels were raised to a lesser degree (p < 0.01). In six patients who had a false positive iCT response after pentagastrin or had raised basal iCT levels measured with a two-site immunoradiometric assay, RR-CGRP showed only a minimal change. On the other hand, in patients with CCH (true positive, n = 8), iCT was increased by only 40% after pentagastrin but RR-CGRP levels rose by 140% (p < 0.001). No change in iCT or RR-CGRP levels in plasma were detected in healthy normal volunteers after administration of pentagastrin. Therefore, in addition to the plasma iCT levels, RR-CGRP would resolve some of the difficult diagnostic problems associated with MTC and likely improve the specificity and sensitivity of identifying CCH.

Expression of calcitonin gene-related peptide in medullary thyroid cancer

We studied the expression of calcitonin (CT) and calcitonin gene-related peptide (CGRP) in 18 patients with medullary thyroid cancer (MTC) in the neoplastic (primary or metastatic) tissue by immunohistochemistry and in the plasma by radioimmunoassay. CT immunoreactivity was found in 100% of the primary and metastatic MTC, CGRP was expressed in 66% of the primary tumors and in 73% of the metastases. Both the number of positive cells and the degree of staining were always higher for CT than for CGRP staining. While plasma CT concentrations were always increased in patients with metastases, 3 patients with metastases had undetectable plasma CGRP levels. A positive correlation was found between plasma CT and CGRP levels. These data indicate that CGRP is frequently expressed in MTC sections and that plasma CGRP measurement is an additional marker for MTC, although has no advantage with respect to CT measurements in monitoring the progression of the disease.

PCR amplification of CGRP II mRNA. Variable expression in tumoral and non-tumoral human thyroid

Two genes code for calcitonin gene-related peptides (CGRPs). One expresses by tissue-specific alternate splicing calcitonin and CGRP I mRNAs, the other CGRP II mRNA. Calcitonin is the marker of sporadic or hereditary human medullary thyroid carcinoma (MTC). CGRP II expression is not well established in normal or tumoral thyroid. After amplification by polymerase chain reaction, CGRP I and II mRNAs were detected in six cases of MTC associated with other endocrine neoplasia (MEN IIa) and in two cases of isolated MTC. CGRP I was detected in all non-C cell tumoral thyroids (6 samples), CGRP II was barely detectable in three out of six cases. CGRP II could be a specific tumoral marker of MTC.

In-situ analysis of calcitonin and CGRP expression in medullary thyroid carcinoma

A combination of immunocytochemistry (ICC) and in-situ hybridization (ISH) applied to formalin-fixed tissue sections was used to analyse the differential expression of calcitonin and CGRP genes, at both peptide and mRNA levels, in normal and neoplastic human thyroid C cells. Calcitonin peptide was readily detectable in normal C cells but its abundance in the neoplastic C cells of medullary thyroid carcinoma (MTC) was reduced in correlation with the degree of tumour differentiation. Conversely, the content of calcitonin mRNA was higher in MTC than in normal C cells and was not significantly related to tumour differentiation. Both the peptide and mRNA of CGRP were present at much lower levels than those of calcitonin in normal C cells but were increased in neoplastic C cells. We conclude that neoplasia of thyroid C cells is associated with (i) an increase in the content of CGRP mRNA and peptide relative to that of calcitonin, consistent with a defect in control of transcript processing, and (ii) a decrease in the ratio of calcitonin peptide to mRNA abundance relative to the normal, suggesting a defect in synthesis or storage of the peptide. ISH analysis of calcitonin mRNA may therefore be a very valuable addition to ICC analysis of the peptide as a diagnostic and prognostic marker for MTC.

Quantification of intracellular calcitonin gene transcripts in human medullary thyroid carcinoma (MTC) by in situ hybridization

The human calcitonin gene generates 2 distinct mature mRNAs by alternative RNA processing, encoding calcitonin (CT) in thyroid C-cells or a neuropeptide (CGRP) in the brain. We evaluated quantitatively by in situ hybridization the expression of the CT gene in tissue section of 5 MTCs (2 sporadic and 3 familial forms). The primary tumor of one MTC was compared to a brain metastasis. In situ hybridization was carried out with tritiated cDNA probes coding for CT and CGRP mRNA. After autoradiography the number of silver grains was counted in 400 cells by computerized analysis of digitized images and expressed as the labelling level (L.L. = grain area/cell area per day of autoradiographic exposure). This was used to calculate the relative abundance per cell of the specific messengers studied, which depends on the autoradiographic efficiency and the specific activity of the probe used. The CT mRNA content was 3.25-6.55 10(-10) micrograms equivalents in the 3 familial forms of MTC and 4.95-9.25 10(-10) micrograms equivalents for the 2 sporadic forms. The levels of CT mRNA in the brain metastasis and in the primary tumor were identical (4.10 10(-10) micrograms equivalents). CGRP mRNA expression was weaker in the sporadic and in the familial thyroid tumors (0.60-1.65 10(-10) micrograms equivalents). The content of mRNA CGRP in the brain metastasis (0.60 10(-10) micrograms equivalents) was lower than that in the primary tumor (1.05 10(-10) micrograms equivalents).(ABSTRACT TRUNCATED AT 250 WORDS)

The utility of some modern techniques in understanding thyroid pathology

A number of evaluating techniques have moved from the research laboratory into the purview of the diagnostic pathologist and have been applied to the analysis of thyroid lesions. Some of these have already proved diagnostically and prognostically useful, whereas some have produced insights into pathogenesis of specific thyroid lesions and disorders. Rapid proliferation and application of these techniques should allow for increased understanding of human thyroid disease in the near future.

Histochemical detection of the messenger RNAs coding for calcitonin and calcitonin gene-related peptide in medullary thyroid carcinomas with radioactive and biotinylated oligonucleotide probes

The present study has been undertaken to investigate the efficiency of biotinylated synthetic oligonucleotide probes in detection by in situ hybridization of the mRNAs coding for calcitonin (CT) or calcitonin gene-related peptide (CGRP) in human medullary thyroid carcinomas (MTCs). Tissue sections fixed with formaldehyde were hybridized with 45-base long oligonucleotides, specific for CT or CGRP mRNA. Recombinant DNA probe or synthetic oligonucleotides radioactively labelled with 32P or 35S were used as controls to detect by autoradiography the corresponding mRNAs in the tumour cells. Oligonucleotide probes labelled by fixation of one biotin molecule at their 5'-end, or by incorporation of a tail of biotin-11-dUTP at their 3'-end, were used and were revealed by incubation with streptavidin-alkaline phosphatase associated with the corresponding substrate. Each biotinylated probe stained exclusively the cytoplasm of the tumour cells, the CT probe giving a much higher level of staining than the CGRP probe. The same cells were found to contain CT and CGRP mRNAs. Controls performed with either radioactive or biotinylated probes confirmed the specificity of the staining. These results demonstrate that biotinylated synthetic oligonucleotides can be used as efficient tools to investigate gene expression in tissue sections, thus avoiding the various inconveniences connected with the use of radioactive probes, especially bio-hazards, the use of autoradiography, the limited histological resolution, and the delay in obtaining results.

Immunohistochemical analysis of calcitonin and calcitonin gene-related peptide in human lung

Calcitonin and calcitonin gene-related peptide (CGRP) have been localized immunohistochemically in neuroendocrine cells of normal and diseased human lungs. Cells immunoreactive for calcitonin and CGRP first appeared in immature bronchi in the 27th gestational week. Thereafter, both peptides were found in the same bronchial neuroendocrine cells throughout fetal and neonatal life. In adult lungs with or without neuroendocrine cell hyperplasia, only calcitonin was present. In 17 of 18 (94%) pulmonary tumorlets, variable numbers of calcitonin-positive cells were identified. A few CGRP immunoreactive cells, as a subset of calcitonin-containing cells, were found in only three (17%) lesions. Of 37 bronchial carcinoids, calcitonin was detected in 14 and CGRP was detected in 16 (38% and 43%, respectively), and both peptides were predominantly localized in the same cells. Ten of 45 (22%) small cell lung carcinomas were calcitonin-immunoreactive. CGRP was noted in only one (2%) of these tumors, and both peptides coexisted in single cells. These findings indicate that the patterns of calcitonin/CGRP expression in hyperplastic bronchial neuroendocrine cells, pulmonary tumorlets, and, to some extent, small cell lung carcinomas are similar to those of normal adult lungs. On the other hand, calcitonin/CGRP expression in bronchial carcinoids is similar to that of late fetal and neonatal lungs.

Ultrastructural and electron immunohistochemical features of medullary thyroid carcinoma

An ultrastructural study, both morphological and immunohistochemical, has been carried out on eight thyroglobulin-positive and nine thyroglobulin-negative medullary carcinomas of the thyroid. The morphometric analysis of granule size showed that all tumours contained cells with small granules and cells with medium size granules, whereas eight tumours had additional cells with large granules. The small granules had an electron dense core, while the medium and large sized granules were both pale-cored and dense-cored. The cells with small, medium or large secretory granules were all immunoreactive for calcitonin and CGRP. No ultrastructural differences were observed between thyroglobulin-positive and thyroglobulin-negative cases of medullary carcinoma of the thyroid.

Ectopic hormone production by a prostatic small cell carcinoma xenograft line

The xenograft line, UCRU-PR-2, has been characterized further. Established from a primary human undifferentiated small cell carcinoma of the prostate, it has been maintained as a stable xenograft line in nude mice and is currently in passage 9. The tumor has maintained the features of small cell undifferentiated carcinoma but shows epithelial as well as neuroendocrine characteristics. In this paper, we describe synthesis and secretion of peptide hormones, ACTH, beta-endorphin and somatostatin in vivo and ACTH and beta-endorphin in vitro by the tumor, UCRU-PR-2. This suggests that the gene for proopiomelanocortin is expressed and that processing of the molecule occurs. This line may yield insights into the histogenesis of the subtypes of prostate cancer, and also aid studies of regulation of ectopic hormone production.

Use of molecular probes in the study of endocrine diseases

DNA hybridization techniques are now commonly used in studies of endocrine disease. Although solution and filter hybridization have been more widely used in endocrine studies, ISH offers many advantages to the pathologist. Individual cells can be visualized directly with the microscope to study the expression of specific gene products. ISH is somewhat similar to immunohistochemistry and can be set up rapidly in most histology laboratories, especially when nonradioactive biotinylated probes are used. The ability to combine ISH with immunochemical techniques offers to the pathologist the use of two powerful diagnostic tools simultaneously. Although DNA hybridization has only begun to have an impact in diagnostic pathology, many studies using this technique in the diagnosis of endocrine diseases are emerging. The availability of more probes, especially with nonradioactive detection systems, should accelerate the application of these techniques in diagnostic pathology. As the number of molecular probes available for hybridization studies increases, pathologists can have a major impact in this field by carefully evaluating probes that have potential diagnostic value for their specificity and sensitivity in a wide variety of normal and abnormal human tissues. Such careful and critical analyses will contribute greatly to the confidence with which these molecular probes can be used as another tool in the analysis of difficult diagnostic lesions. Molecular hybridization techniques will also contribute greatly to our knowledge of basic biology and pathophysiology in the study of abnormal gene expression in endocrine and other pathologic conditions.

Hybridization histochemistry

The location of gene expression by hybridization histochemistry is being applied in many areas of research and diagnosis. The aim of this technique is to detect specific mRNA in cells and tissues by hybridization with a complementary DNA or RNA probe. Requirements for optimal specificity, sensitivity, resolution and speed of detection may not all be encompassed in one simple technique suitable for all applications, thus appropriate procedures should be selected for specific objectives. With reference to published procedures and our own extensive experience, we have evaluated fixatives, probes, labels and other aspects of the technique critical to the preservation and hybridization in situ of mRNA and detection and quantitation of hybrids.

Preparation of base-modified nucleosides suitable for non-radioactive label attachment and their incorporation into synthetic oligodeoxyribonucleotides

A very mild and efficient procedure has been developed for the preparation of C-5 substituted deoxyuridines. The substituent carries a masked primary aliphatic amino group. These compounds are readily converted into their phosphoramidites and can be used to prepare oligonucleotides carrying one or more aliphatic amino groups. Fluorescein isothiocyanate coupled to these compounds gives oligonucleotide probes carrying multiple fluorescein labels. These compounds have a free 5'-hydroxy group enabling additional 5'- end radioactive labelling for evaluation of their hybridization characteristics. It was found that oligonucleotides carrying a long (11 atom) linker arm to the fluorescein hybridize more efficiently to mRNA than those carrying a short (4 atom) arm. The long linker arm derivatives are comparable to underivatized oligonucleotides in hybridizing to mRNA.

Basal and stimulated release of calcitonin gene-related peptide (CGRP) in patients with medullary thyroid carcinoma

Calcitonin gene-related peptide (CGRP) is a recently discovered peptide whose existence was first predicted following sequence analysis of the rat calcitonin gene. In the present study, plasma levels of CGRP were measured in patients with medullary thyroid carcinoma, both basally and following calcium or pentagastrin stimulation. Using a sensitive radioimmunoassay for CGRP, 19 of 21 patients with medullary thyroid carcinoma had elevated plasma levels of immunoreactive CGRP (median value 114 pmol/l) while 23 normal subjects had plasma CGRP levels below the detection limit of the assay (less than 10 pmol/l). Calcium or pentagastrin infusion in medullary thyroid carcinoma patients were potent stimuli to CGRP release, increasing plasma levels two- to five-fold. Chromatographic characterization using high pressure liquid chromatography of the CGRP immunoreactivity in plasma from two patients with medullary carcinoma of the thyroid demonstrated the presence of two molecular forms, neither of which co-eluted with synthetic human CGRP. The role of CGRP in the pathophysiology of medullary thyroid carcinoma is not clear but it may contribute to some of the clinical features associated with the disease. Furthermore, measurement of CGRP in conjunction with calcitonin could help in determining the prognosis of these patients.