The role of hyperplasia in multiple parathyroid adenomas

BACKGROUND: Parathyroid adenoma is the most common cause of primary hyperparathyroidism (pHPT). Adenomas usually involve only a single gland, and the remaining glands are normal or suppressed. Multiple parathyroid adenomas have been reported to occur in as high as 11% of patients with pHPT. The significant incidence of multiple adenomas with histologic similarities to hyperplasia has raised the possibility that adenoma is a continuation of the hyperplasia state. To test this theory, we used molecular genetics to compare clonality and proliferative activity of parathyroid adenoma with its corresponding normal glandular tissue. Furthermore, we devised a scheme to definitively distinguish between the different parathyroid states on a molecular level, because histologic distinction is unreliable. METHODS: The study included three patients with a diagnosis of singular parathyroid adenoma and three with double parathyroid adenomas. Paraffin-embedded surgical specimens of both adenomas and normal glands were retrieved from each patient. Clonal analysis of the phosphoglycerolkinase (PGK) gene has suggested that parathyroid adenomas are monoclonal. Clonality of parathyroid adenomas and normal parathyroid glands was studied by polymerase chain reaction-based restriction fragment length polymorphic analysis for the PGK gene. Proliferative activity of the specimens was also analyzed using the immunohistochemical markers PCNA and Ki-67. RESULTS: All adenomas were monoclonal and all normal parathyroid glands were polyclonal for the PGK gene in both the single and double adenoma specimens. All adenomas stained positive for proliferative activity. In the three patients with singular adenoma, proliferative activity was not detected in the normal parathyroid tissue. However, in the double adenoma group, two of the three patients showed hyperproliferative activity in the normal glands. CONCLUSION: Proliferative activity consistent with hyperplasia was present in some normal glands of multiple adenoma patients. Our observation supports the theory that multiple adenomas may be a continuation of the hyperplasia state.     

Hyperparathyroidism in multiple endocrine neoplasia syndrome.

BACKGROUND. We analyzed clinical findings and results of parathyroidectomy in 42 patients treated from 1936 to 1988 at the University of California, San Francisco (UCSF) for primary hyperparathyroidism and multiple endocrine neoplasia (MEN) syndrome to document results of parathyroidectomy and reasons for failed parathyroid operations. METHODS. Of the 42 patients (38 had MEN 1 syndrome; 4 had MEN 2A syndrome), 40 patients were treated surgically: 29 had initial parathyroidectomy at UCSF; 11 were referred to UCSF because of MEN syndrome. Eight of these 11 patients required reoperation for persistent or recurrent hyperparathyroidism. Patients with hyperplasia were treated with subtotal parathyroidectomy; the glands of those patients with solitary or double adenomas were removed with or without biopsy of the normal appearing glands. RESULTS. Overall, in seven (50%) of 14 patients with hyperplasia, three (16%) of 19 patients with solitary adenoma, and one (14%) of seven patients with double adenomas, recurrent or persistent hyperparathyroidism developed. Failure in patients with hyperplasia was due to missed supernumerary glands (13%) and missed ectopic glands (33%). Failure occurred in patients with solitary (three patients) or double (one patient) parathyroid tumors because of unrecognized hyperplasia. None of the four patient with MEN 2A syndrome had persistent or recurrent disease, but hypoparathyroidism developed in one patient; hypoparathyroidism developed in three patients with MEN 1 syndrome. CONCLUSIONS. These data suggest that although many patients with primary hyperparathyroidism and MEN syndrome have multiple abnormal parathyroid glands, two populations of patients exist; one population has solitary or double adenomas and recurrence is uncommon, whereas the other population of patients has hyperplasia and persistent or recurrent disease is common.     

Early postoperative function of suppressed parathyroid glands with microscopic hyperplasia

Calcium-parathyroid hormone (Ca-PTH) relationships were studied perioperatively in 35 patients with primary hyperparathyroidism. Twenty-nine patients had solitary adenomas that caused preoperative hypercalcemia; those patients whose remaining glands were subjected to biopsy were classified as having either microscopic evidence of suppression in those glands (15 patients) or no evidence of suppression (less than or equal to 30% stromal fat on biopsy cross sections, 11 patients). Before surgery, all patients showed the expected positive slopes for Ca-PTH linear regression curves. After surgery, all patients with adenomas showed an immediate and sustained shift of the Ca-PTH regression to the right; this shift achieved statistical significance only in those patients whose remaining glands showed microscopic evidence of suppression (greater than 30% fat, p less than 0.05). Moreover, the slope of the Ca-PTH regression curve for these patients assumed a negative value 1 month after surgery. All patients with adenomas were eucalcemic after surgery, regardless of the cellularity of the remaining in situ glands. We conclude that the absence of microscopic suppression in grossly suppressed parathyroid glands at the time of adenoma resection for hyperparathyroidism does not affect postoperative results. However, the presence of microscopic hyperplasia in macroscopically normal or suppressed glands may represent a persistent alteration in biologic function, evidenced by failure of these glands to achieve negative calcium regulation.     

A new method with high sensitivity and specificity for localization of abnormal parathyroid glands.

A novel method for localization of abnormal parathyroid glands involving color-processing of nuclear scintigrams of the neck after injection of Thallium-201 and Technetium pertechnetate is presented with surgical correlation. Preoperative localization of single parathyroid adenomas was successful in 88% of previously unoperated patients and in 85.7% of those with adenomas not located at previous surgery. Eighty-three per cent of glands with secondary hyperplasia, 66% of glands with primary hyperplasia, and one carcinoma were localized. No abnormal studies were seen in non-hyperparathyroid hypercalcemia, and no false positive studies were seen. Localization appeared related to larger adenomas (300-5000 mg), although one of 60 mg was localized. Color-comparison dual-isotype scintigraphy was useful for localization of parathyroid adenomas and hyperplastic glands and exceeded the reported sensitivity of either ultrasonography or computerized tomography. It deserves wider evaluation in preoperative management of at least hyperparathyroidism of the primary or persistent types.     

Ultrasound scanning for preoperative location of parathyroid tumours

Ultrasonic examination of the parathyroid glands has been used in 50 consecutive patients with surgically verified hyperparathyroidism. It revealed 21 of 32 parathyroid adenomas located in the neck. In 16 patients with primary or secondary (uraemic) hyperplasia, 11 out of 48 hyperplastic glands in the neck were identified by ultrasound. A parathyroid adenoma was revealed in all (3) patients with hypercalcaemic crisis. Enlarged parathyroid glands were correctly located in all (5) patients with adenomas and previous explorations of the neck, whereas two out of three glands were visualized by ultrasound prior to secondary explorations in 3 patients with hyperplasia associated with the multiple endocrine neoplasia syndrome type 1. Undetected parathyroid glands were generally smaller than those visualized by ultrasonic examination. It was often difficult to unequivocally establish that identified lesions represented parathyroid glands. Irregular noduli and cysts of the thyroid as well as lymph nodes could be misinterpreted as parathyroid lesions. A nodular thyroid goitre was present in almost half of the patients with a negative ultrasonic examination of the parathyroid glands.     

Double parathyroid adenomas. Clinical and biochemical characteristics before and after parathyroidectomy.

OBJECTIVE: There is considerable debate about whether double parathyroid adenomas are a discrete entity or represent hyperplasia with parathyroid glands of varying sizes. This distinction is important because it impacts on the extent of parathyroid resection and the success of the parathyroid operation. SUMMARY BACKGROUND DATA: Double parathyroid adenomas have been reported to occur in 1.7% to 9% of patients with primary hyperparathyroidism (HPT). It is important for surgeons to differentiate between double adenoma and hyperplasia with glands of varying sizes using gross examination during the initial procedure because microscopic findings of a small biopsy specimen at frozen-section examination may not be diagnostic. METHODS: From 1982 to 1992, 416 unselected patients (309 women and 107 men) with primary HPT without familial HPT or multiple endocrine neoplasia (MEN) were treated by one surgeon at the University of California at San Francisco. Double adenoma occurred in 49 patients, solitary adenoma in 309 patients, and hyperplasia in 58 patients. The authors analyzed the clinical manifestations, the preoperative and postoperative serum levels of calcium, phosphate, and parathyroid hormone (PTH), and the success rate and outcome after parathyroidectomy and compared their results in 49 patients with double adenomas to the results for patients with solitary adenomas or hyperplasia. RESULTS: Ten of the patients with double adenomas (20.4%) were referred for persistent HPT after removal of one abnormal parathyroid gland. The ages of the patients with double adenoma, single adenoma, and hyperplasia were 61 +/- 14, 56 +/- 15, and 58 +/- 7 years, respectively. Fatigue, muscle weakness, and bone pain were common in patients with double adenomas, whereas nephrolithiasis occurred more frequently in patients with solitary adenoma (p = 0.0001). Serum calcium and PTH levels (per cent of upper limit of normal) fell from 11.5 +/- 1.2 mg/dL and 487% to 9.5 +/- 0.8 mg/dL and 61% for patients with double adenomas; from 11.9 +/- 0.9 mg/dL and 378% to 9.3 +/- 1.4 mg/dL and 101% for patients with single adenoma; and from 10.9 +/- 0.5 mg/dL and 418% to 9.1 +/- 0.7 mg/dL and 94% for patients with hyperplasia, respectively. There was no recurrence in the patients with double adenomas with a mean follow-up time of 5.8 years. CONCLUSIONS: Double adenomas are a discrete entity and occur more often in older patients. Patients with double adenomas can be successfully treated by removal of the two abnormal glands.     

Multiple parathyroid adenomas: report of thirty-three cases

An increasing number of patients with primary hyperparathyroidism are found to have two or three enlarged parathyroid glands. Of 865 patients successfully operated on by one surgeon (J.N.A.), multiple enlarged parathyroid glands (adenomas) were found and resected in 33 cases (3.8%), with resulting normocalcemia lasting from 1 to 22 years (mean 5.8). Twenty-nine patients had two adenomas and four had three adenomas. In 28 patients the multiple adenomas were synchronous. Twenty-five patients underwent removal of all of the enlarged parathyroid glands in one operation; in three patients one adenoma was removed, reoperation for persistent hypercalcemia was performed, and a second adenoma was resected with cure. In five patients one adenoma was removed, normocalcemia ensued for 3 to 18 years, and a second (metachronous) adenoma occurred and was resected successfully. Although 10 of 70 enlarged parathyroid glands removed were labeled hyperplasia, cure in all but one of our patients by selective resection of only enlarged parathyroid glands emphasizes the unreliability of histologic criteria in differentiating between parathyroid adenoma and hyperplasia. Based on this study, we support the existence of multiple adenomas and advocate removal of only macroscopically enlarged parathyroid glands in patients with primary hyperparathyroidism.     

Clinical characteristics and surgical treatment of sporadic primary hyperparathyroidism with emphasis on chief cell hyperplasia

In 570 patients with sporadic primary hyperparathyroidism, the age, sex, symptoms, and preoperative serum calcium values were related to the histopathologic diagnoses, operative findings, and the extent and outcome of parathyroid surgery. Renal stone formation was especially prevalent in younger patients with slight hypercalcemia and parathyroid chief cell hyperplasia, whereas neuromuscular and psychiatric disturbances were overrepresented among older women with higher serum calcium values. Serum calcium concentration was inversely correlated to the proportional incidence of chief cell hyperplasia and positively correlated to the glandular weight of both adenomas and hyperplasias. Glandular size was markedly irregular in chief cell hyperplasia, with increased gland weights of no more than two glands in 78% of patients. During follow-up, for as long as 27 years, normocalcemia was obtained in 91% of patients with adenomas, with failures mainly depending on difficulties in identifying the parathyroid glands. The rate of normocalcemia was lower (80%) among patients with hyperplasia, but an inability to visualize the glands was not a major cause of failure. In patients with hyperplasia with asymmetric and more markedly enlarged glands, it appeared sufficient to remove only the enlarged glands, whereas the findings advocated a subtotal 3- to 3.5-gland resection in patients with more symmetrically or less enlarged hyperplastic glands.     

Blood Supply and Parathyroid Hormone Secretion in Pathological Parathyroid Glands

The blood supply of pathologic parathyroid glands and the relation between parathyroid hormone secretion and parathyroid blood perfusion was studied during surgery for hyperparathyroidism. Blood flow in 39 single adenomas and 20 glands classified as primary or secondary hyperplasia were studied intraoperatively with laser Doppler flowmetry. The ipsilateral inferior thyroid artery was occluded during continuous flowmetry recording, which resulted in a 40% reduction of parathyroid blood flow in both groups. In 12 patients with single adenomas, intact parathormone (iPTH) was measured intraoperatively before and during occlusion of the ipsilateral inferior thyroid artery and after extirpation of the adenoma. During occlusion the iPTH levels were mainly unchanged despite blood flow reduction of up to 80%. After removal of the adenoma the iPTH normalized within 15 minutes. In a control group of eight single adenomas, iPTH was measured similarly without vascular occlusion, demonstrating comparable iPTH levels. This study demonstrates similar routes of vascularization for single adenomas and hyperplastic glands, as was earlier seen for normal parathyroid glands. The increased parathyroid hormone secretion from single adenomas appears to remain mainly unchanged during significant blood flow reduction.     

Preoperative imaging of abnormal parathyroid glands in patients with hyperparathyroid disease using combination Tc-99m-pertechnetate and Tc-99m-sestamibi radionuclide scans.

OBJECTIVE: To evaluate the efficacy of combined Tc-99m-pertechnetate and Tc-99m-sestamibi radionuclide scanning for imaging abnormal parathyroid glands in hyperparathyroid disease in a prospective study. SUMMARY BACKGROUND DATA: Established methods to localize abnormal parathyroid glands lack accuracy for routine use. Tc-99m-sestamibi used in conjunction with iodine-123 has excellent potential for preoperative imaging in patients with hyperparathyroid disease. An alternative method for parathyroid imaging was studied using Tc-99m-pertechnetate and Tc-99m-sestamibi. METHODS: Thirty patients with hyperparathyroid disease had Tc-99m-pertechnetate and Tc-99m-sestamibi subtraction radionuclide scanning to visualize abnormal parathyroid glands before surgery. The patients had surgery and pathologic confirmation of all parathyroid glands. RESULTS: In 23 patients with primary hyperparathyroidism, 12 of 13 solitary adenomas were visualized. Six of nine patients with diffuse hyperplasia had bilateral uptake consistent with diffuse hyperplasia. Three of nine patients had negative scans. One patient previously operated on for diffuse hyperplasia had only one gland scanned. Seven patients with renal failure-associated hyperparathyroid disease were scanned: five had bilateral uptake of Tc-99m-sestamibi consistent with hyperplasia, and two who had been previously operated on had localization of remaining abnormal parathyroid glands. CONCLUSIONS: Tc-99m-pertechnetate combined with Tc-99m-sestamibi subtraction radionuclide scanning is less cumbersome to implement than iodine-123 combined with Tc-99m-sestamibi scanning. It has a high sensitivity for imaging solitary parathyroid adenomas or persistent solitary hyperplastic glands. However it does not have the resolution necessary to delineate all parathyroid glands in diffuse hyperplasia.     

Relation of biochemical, cytologic, and morphologic parameters to the result of gammagraphy with technetium 99m sestamibi in primary hyperparathyroidism

The aim of this study was to analyze the possible relation of biochemical, cytologic, and morphologic parameters to the results of parathyroid gammagraphy with Tc 99m sestamibi in primary hyperparathyroidism. We studied 46 consecutive patients with primary hyperparathyroidism who were undergoing surgery. All the patients were given a preoperative parathyroid gammagraphy with Tc 99m sestamibi and a complete preoperative biochemical study. During the surgical intervention we recorded the weight and size of the pathologic glands to calculate the volume of each. We also determined the percentage of the chief and oxyphil cells in the pathologic glands. Tc 99m sestamibi sensitivity is higher in adenomas (91%) than in hyperplasia (67%) or double adenomas (50%). No relation was found between biochemical or cytologic parameters and gammagraphic results. Weight and gland volume were significantly greater for adenomas than for hyperplasia (P < 0.0014 and P < 0.0004, respectively), and statistically significant differences in both of them were observed between the glands with positive and negative sestamibi.     

Intracellular lipid droplets in functioning transitional parathyroid oxyphil adenomas. A caveat.

Histochemical demonstration of intracellular lipid droplets on frozen section has been used to distinguish normal parathyroid tissue from that of adenoma and chief cell hyperplasia. Differentiation is based on the observation that the cells of adenoma and chief-cell hyperplasia largely lack intracellular lipid, which is present in the suppressed chief cells of normal glands in patients with adenoma. We present two functional transitional oxyphil adenomas that contained abundant intracellular lipid. Failure to recognize that transitional oxyphilic adenomas may contain focal accumulation of intracellular lipid droplets could lead to confusion in histologic interpretation.     

Late results of operation for primary hyperparathyroidism in 441 patients

The late results of operation for primary hyperparathyroidism (HPT) were analyzed in 441 patients operated on 4 to 27 years earlier (mean follow-up time, 7.7 years). A conservative surgical approach was mainly used, attempting if possible to visualize all four parathyroid glands and extirpate only the enlarged glands. Subtotal resection was performed in patients with hyperplasia. The histopathologic diagnosis was adenoma in 77% and hyperplasia in 18%. In 5% of the patients, the histopathologic classification was uncertain. Hypercalcemia persisted after operation in 8% of all patients. This generally occurred because of an incomplete neck exploration or too limited a resection in the patients with hyperplasia. Recurrent hypercalcemia occurred in 16% of the patients operated on for hyperplasia and was noted 1 to 19 years after surgery. Recurrences were also seen in 3% of the patients with adenomas but not earlier than 9 years after the operation. These findings suggest that primary HPT may even in patients with adenomatous disease, sometimes affect all parathyroid glands. Nevertheless, it was obvious that most of the patients with adenomas would not have benefited from a more radical procedure. On the other hand, it was evidently important to obtain a correct histopathologic diagnosis intraoperatively so that patients with hyperplasia could be identified and adequatley treated.     

The clinical significance and anatomic distribution of parathyroid double adenomas

BACKGROUND: Parathyroid double adenomas are reported to occur in 3% to 12% of cases of primary hyperparathyroidism, but the very existence of double adenomas has been controversial. This study was undertaken to evaluate the clinical significance and anatomic distribution of parathyroid double adenomas. STUDY DESIGN: The medical records of 384 consecutive patients who underwent operation for primary hyperparathyroidism were reviewed. RESULTS: A total of 27 patients (7%) were found to have double parathyroid adenomas. Intraoperative parathyroid hormone (PTH) levels were measured in each case. Two enlarged hypercellular parathyroid glands were identified in 6 possible configurations: 10 both superior, 3 both inferior, 5 both right, 3 both left, 5 right superior and left inferior, and 1 left superior and right inferior. There was preferential distribution to the bilateral superior position (p = 0.008). In all patients intraoperative PTH levels dropped by at least 50% from baseline and into the normal range after removal of both abnormal parathyroid glands. All patients remain normocalcemic 1 to 26 months postoperatively. Two patients have persistently elevated PTH values with normal serum calcium levels. CONCLUSIONS: The drop in intraoperative PTH levels and maintenance of normocalcemia postoperatively confirm previous reports that double adenomas do exist and are not simply missed cases of four-gland hyperplasia. Their incidence is more than would be expected by chance alone. The preferential occurrence of bilateral superior double adenomas suggests the possibility that these may represent hyperplasia of parathyroids arising from the fourth branchial pouch rather than isolated neoplastic events.     

Surgical treatment of primary hyperparathyroidism. Evaluation of 263 cases

A retrospective study of the case-reports of 263 patients explored surgically for primary hyperparathyroidism demonstrated the cause to be: an adenoma (206 cases), a primary hyperplasia (29 cases), or a cancer (3 cases), exploration was negative in 25 cases. Presenting symptoms were mainly urinary, but 15 p. 100 of patients seen during the last two years had been asymptomatic. Nine patients required emergency surgery and 29 had a primary normocalcemic hyperparathyroidism. The two most useful laboratory examinations, apart from measurement of blood calcium and phosphorus levels, were parathormone assay (elevated levels were present in 80 p. 100 of cases) and quantitative bone biopsy (positive in over 80 p. 100 of patients). The surgical approach was mainly cervical, except for repeat operations when ten sternotomies were performed with successful results in 4 cases. Immediate postoperative mortality was quite high (3 p. 100), particularly in the acute forms or those with multiple adenomas, and in patients over 70. Morbidity (hypocalcemia, recurrent nerve palsy) was increased after repeat surgery. Analysis of long-term results, particularly with respect to urinary symptoms, showed marked differences between lesions of single glands (adenoma) and hyperplasia. The most difficult problem to resolve with this surgery is the importance to attach to excision of the parathyroids when lesions are present in several glands.     

Primary bimorphic adrenocortical disease: cause of hypercortisolism in McCune-Albright syndrome

McCune-Albright syndrome (polyostotic fibrous dysplasia, café-au-lait skin spots, and precocious puberty) is a genetically mosaic disorder with populations of mutant and normal cells in affected organs. Cushing syndrome, a rare feature of the condition, usually affects infants and is the result of corticotropin-independent primary bilateral adrenal disease, usually interpreted as nodular adrenocortical hyperplasia. In this study of 9 patients with Cushing syndrome and McCune-Albright syndrome, light microscopy revealed a characteristic bimorphic pattern of diffuse and nodular hyperplasia and a distinctive form of cortical atrophy with apparent zona glomerulosa hyperplasia in 8 patients, all very young. The pattern could be explained by the presence of a mosaic distribution of mutant and normal cells in the adrenal glands. The findings are different from those in inherited or other forms of genetically caused Cushing syndrome. The ninth patient, aged 17 years, had an adrenal adenoma and diffuse cortical hyperplasia in each adrenal gland.     

Oncocytomas of the kidney

Seven cases of oncocytoma of the kidney are reported. In three patients this was the original histological diagnosis; the other four were diagnosed after a review of 165 renal tumours which had been previously diagnosed as carcinoma. The oncocytomas were also analysed by electron microscopy. In one case adenomas of the suprarenal glands were also found.     

Prospective evaluation of delayed technetium-99m sestamibi SPECT scintigraphy for preoperative localization of primary hyperparathyroidism

BACKGROUND: Delayed technetium-99m sestamibi single photon emission computed tomography (SPECT) scans were prospectively analyzed in a large series of patients with primary hyperparathyroidism. METHODS: Three hundred thirty-eight patients underwent sestamibi-SPECT and were explored. Prospective data included preoperative demographics, clinical, sestamibi, and operative findings, laboratory values, and pathologic and follow-up laboratory results from all patients. RESULTS: Between 1994 and 2000, 287 unexplored patients (85%) and 51 re-explored patients (15%) participated. The abnormal parathyroid glands excised from 336 of 338 patients included 299 single adenomas (88%) and 23 double adenomas (7%), and 14 patients had multigland hyperplasia (4%). Sestamibi SPECT correctly lateralized 349 of 400 abnormal parathyroid glands, with an overall sensitivity of 87%, an accuracy of 94%, and a positive predictive value of 86%. Precise localization occurred in 82% of the abnormal parathyroid glands. Sestamibi sensitivity was similar in unexplored (87%) and reoperative (92%) cases; two hundred eighty-six of 299 (96%) solitary adenomas, 38 of 46 (83%) double adenomas, but only 25 of 55 (45%) hyperplastic glands were identified. The mean weight of the true-positive glands (1252 +/- 1980 mg) was greater than that of the false-negative glands (297 +/- 286 mg) (P <.005). Three patients had persistent primary hyperparathyroidism, in spite of the excision of sestamibi-identified lesions in 2 cases. Follow-up indicated curative resection in 99% of the unexplored cases and 94% of the remedial cases. CONCLUSIONS: Sestamibi SPECT is highly accurate for the localization of parathyroid adenomas in unexplored and re-explored cases, where it is often the only imaging required. Its sensitivity is limited in multiglandular disease.     

Parathyroid hyperplasia, adenomas, and carcinomas: differential expression of p27Kip1 protein

The histologic spectrum of proliferative parathyroid lesions (hyperplasia, adenoma, and carcinoma) often overlap, and differentiation between these lesions may at times be difficult. p27kip1 (p27) is a cyclin-dependent kinase inhibitor that helps regulate the transition from the G1 to the S phase of the cell cycle. Significantly higher levels of p27 expression have been detected in some normal tissues than in their neoplastic counterparts. The authors analyzed a series of parathyroid lesions to determine if expression of this cell cycle protein may be useful in distinguishing between parathyroid hyperplasia, adenomas, and carcinomas. Formalin-fixed paraffin-embedded tissues from randomly selected patients (22 histologically normal parathyroid glands, 33 cases of hyperplasia, 43 adenomas, and 17 carcinomas) were analyzed for expression of p27 by immunostaining. All cases were also immunostained for Ki67 with antibody MIB-1. The distribution of immunoreactivity was analyzed by quantifying the percentage of positive nuclei that was expressed as the labeling index (LI). In situ hybridization (ISH) for p27 mRNA was done using a cRNA probe with 30 of these cases. Normal parathyroid glands had the highest p27 LI (89.6 +/- 1.4), followed by hyperplasia (69.6 +/- 7.5), adenomas (56.8 +/- 3.4), and carcinomas (13.9 +/- 2.6). ISH showed no differences in p27 mRNA, indicating that the expression of the p27 gene was controlled at a posttranslational level in parathyroid tissues. Ki67 expression was significantly higher in carcinomas (LI = 8.4 +/- 1.9) than in adenomas (LI = 2.7 +/- 0.2) and hyperplasia (LI = 3.3 +/- 0.4). These results suggest that both p27 and Ki67 may be helpful in the diagnosis of histologically difficult parathyroid lesions.