Radiotherapy for nonfunctional pituitary adenoma: analysis of long-term tumor control

(99m)Technetium pentavalent dimercaptosuccinic acid scintigraphy in the follow-up of clinically nonfunctioning pituitary adenomas after radiotherapy

BACKGROUND

It is still difficult to differentiate pituitary adenoma remnants from postradiotherapy fibrosis by computed tomography (CT) or magnetic resonance imaging (MRI), especially in patients with clinically nonfunctioning pituitary adenomas (NFA), lacking circulating markers to follow disease progression or cure.

OBJECTIVE

We investigated the usefulness of scintigraphy with technetium-99m pentavalent dimercaptosuccinic acid [(99m)Tc(V)DMSA], shown previously to detect most pituitary GH- and PRL-secreting adenomas and NFA, with tumour-to-background ratios (T/B) as high as 25-fold.

PATIENTS

Eighteen patients with NFA (study group), 10 patients with GH- and three patients with PRL-secreting adenomas (control group), all of whom had undergone previous surgery.

DESIGN

The study was an open longitudinal design. Pituitary CT/MRI and (99m)Tc(V)DMSA scintigraphy was performed before and 1, 3 and 5 years after conventional radiotherapy. Tumour size was measured as maximal diameter of the residual lesion, while uptake of (99m)Tc(V)DMSA was measured as a T/B ratio.

RESULTS

At study entry, pituitary (99m)Tc(V)DMSA uptake was found in 13 NFA (72.2%), seven GH-secreting (70%) and all PRL-secreting adenomas; remnant tumour was documented by CT/MRI in all 31 patients. Maximal remnant diameter was significantly higher in patients with positive (13.3 +/- 0.9 mm) than in those with negative scintigraphy (7.0 +/- 0.3 mm, P < 0.001). During the 5-year follow-up postradiotherapy, a significant decrease in (99m)Tc(V)DMSA uptake (9.7 +/- 0.8 vs. 3.2 +/- 0.5, P < 0.0001) occurred in all but three patients. Two NFA patients died of tumour invasion 19 and 36 months after radiotherapy and one acromegalic patient had no change in his hormone levels. In the eight negative patients (five NFA and three GH), scintigraphy remained negative throughout follow-up. A remarkable shrinkage of the remnant tumour was observed in both the patients with negative (from 7.0 +/- 0.3 to 1.9 +/- 0.6 mm, P < 0.001) and in those with positive scintigraphy (from 13.3 +/- 0.9 to 7.3 +/- 0.6 mm, P < 0.001). At the end of the study, CT/MRI showed evident remnant tumour in 13 of 16 NFA (81.2%), nine GH-secreting (90%) and all three prolactinomas (100%), while the scintigraphy was negative (T/B < 1) or faintly positive (T/B 1-2) in eight of 16 NFA (50%), five GH-secreting (50%) and one prolactinoma (33.3%).

CONCLUSIONS

Functional imaging of pituitary remnant adenomas (> 10 mm in size) by (99m)Tc(V)DMSA depicts viable pituitary adenoma remnants. This approach may be of clinical value in patients with clinically nonfunctioning adenomas to monitor the effects of radiotherapy.

Medical therapy of gonadotropin-producing and nonfunctioning pituitary adenomas

Clinically nonfunctioning pituitary adenomas are one of the most common types of pituitary tumors. Unless they present with symptoms related to local mass effect, most tumors are detected incidentally when imaging studies are performed for other reasons. Although clinically nonfunctioning, most of these tumors have evidence, in vitro, of gonadotropin hormone or glycoprotein subunit production. The gonadotropins or their monomer submits rarely cause clinically identifiable effects. When these tumors present as macroadenomas, often with associated mass effect and hypopituitarism, primary therapy is neurosurgery. The role for medical therapy will be reviewed here.

Are nonfunctioning pituitary adenomas extending into the cavernous sinus aggressive and/or invasive?

OBJECTIVE

We studied nonfunctioning pituitary adenomas extending to the cavernous sinus to gain insight into the discrepancy between their histologically benign nature and frequent extension into the cavernous sinus.

METHODS

We studied 10 patients with nonfunctioning pituitary adenomas that completely encircled the cavernous carotid artery (extension group). All 10 patients underwent surgery to remove intrasellar and/or suprasellar parts of the adenomas. Ten patients with nonfunctioning pituitary adenomas without cavernous sinus extension comprised the control group. Tumor size follow-up data were obtained by magnetic resonance imaging. Immunostaining was performed for Ki-67, cathepsin B, and matrix metalloprotainase-9. To assess the wall thickness, 10 cavernous sinuses were removed from the cranial base of adult cadavers, and the walls were examined histologically.

RESULTS

Magnetic resonance imaging demonstrated no remarkable growth in most of the patients during the follow-up period (mean, 65.8 mo). There was no statistical difference in Ki-67, cathepsin B, and matrix metalloprotainase-9 immunostaining between the extension group and the control group. The cadaver study demonstrated that the medial wall was significantly thinner than the superior and the lateral walls (P < 0.0005). We found small defects in the capsule histologically in 3 of 30 sections.

CONCLUSION

Our results indicate that most of nonfunctioning pituitary adenomas extending into the cavernous sinus are neither aggressive nor invasive. The high incidence of cavernous sinus extension of benign adenomas may be caused by the weakness of the medial wall of the cavernous sinus.

Endocrine inactive and gonadotroph adenomas: diagnosis and management

Endocrine inactive pituitary adenomas represent about one quarter of all pituitary tumors. By immunocytochemistry, most of these tumors are positive for intact gonadotropins and/or their subunits. Clinical presentation is usually secondary to mass effect symptoms, such as visual disturbances, headache, and hypopituitarism. Differential diagnosis is usually accomplished by neuroradiologic studies, even though in selected cases positron emission tomography and/or single photon emission tomography may aid to distinguish pituitary adenomas from other endocrine inactive lesions, such as meningiomas and craniopharyngiomas. Surgical management is usually considered the first choice treatment for patients with endocrine inactive pituitary adenomas because it is very effective in ameliorating symptoms of chiasmal compression and headache. Radical removal of the tumor, however, is difficult to obtain because of the frequent invasiveness into the cavernous sinus. Radiation therapy diminishes the likelihood of tumor recurrence, especially in patients with demonstrable tumor remnants after surgery. Medical therapy with dopaminergic drugs, somatostatin analogs, or gonadotropin-releasing hormone agonists or antagonists causes mild reduction of tumor size in few patients and, therefore, seems to be of limited value in the therapeutic management of patients with endocrine inactive pituitary adenomas.

Growth promoting effect of human plasma ultrafiltrate bioactive fraction (TBP) for human non-functioning pituitary adenoma cells in vitro

We described before that the chromatographically purified "human plasma ultrafiltrate bioactive fraction" (humoral factor tentatively denoted as tumor basic protein--TBP) regulates in vitro release of ACTH from pituitary adenomas stimulating the hormone release from the tumors showing low hormonal activity in vitro and inhibiting ACTH production in vitro by highly hormonally active pituitary tumors. In this study we describe growth promoting effects (determined by 3H-TdR incorporation assay) of TBP (5 microg/l, i.e. 10% w/v plasma equivalent concentration) for 10 non-functioning pituitary tumors. The effects of TBP appeared to negatively correlate with the in vitro growth abilities of the tumors that were otherwise dependent on the duration of the clinical symptoms of the tumor presence. Hence, similar to its effects on hormonal activity of the pituitary tumors, TBP stimulated the growth of the tumors which did not express high spontaneous 3H-TdR intensity, but did not stimulate the cells with high capacity of spontaneous 3H-TdR incorporation. Moreover, all the tumors that were stimulated by TBP were nononcocytic adenomas while oncocytoma cells were not stimulated at all. Thus, TBP shows activity of humoral (plasma) factor involved in the growth regulation of pituitary adenomas that might be used to define the growth abilities of these tumors, especially in case of null cell adenomas and oncocytomas as were the tumors used in this study.

Stereotactic conformal radiotherapy for pituitary adenomas: technique and preliminary experience

OBJECTIVE

Stereotactic conformal radiotherapy (SCRT) is a high precision technique of fractionated radiotherapy which ensures accurate delivery of radiation with reduction in the volume of normal tissue irradiated as compared to conventional external beam radiotherapy. We describe the technique and preliminary experience of SCRT in patients with residual and recurrent pituitary adenomas.

PATIENTS AND METHODS

Between February 1995 and March 1999, 22 patients (mean age: 45.3, range: 20-67 years) with residual or recurrent pituitary adenomas (13 nonfunctioning, nine secretory) were treated with SCRT. All were immobilized in a relocatable Gill-Thomas-Cosman (GTC) frame and tumour was localized on a postcontrast planning computerized tomography (CT) and MRI scan. The gross tumour volume (GTV) and the critical structures were outlined on contiguous 2-3 mm separated slices. A margin of 5 mm (12 patients) to 10 mm (10 patients) was grown around GTV in three-dimensions (3-D) to generate the planning target volume (PTV). The treatment was delivered by three (five patients) and four (17 patients) maximally separated conformal fixed fields with each field conformed to the shape of the tumour using customized lead alloy blocks (19 patients) or multileaf collimator (three patients). The patients were treated on a 6-MV linear accelerator to a dose of 45 Gy in 25 fractions (18 patients) and 50 Gy in 30 fractions (four patients).

RESULTS

The technique of SCRT has become a part of the routine work of the radiotherapy department. The treatment was well tolerated with minimal acute toxicity. One patient developed transient quadrantanopia 2 weeks after treatment with full recovery after a short course of corticosteroids. One patient had a transient visual deterioration 7 months after treatment due to cystic degeneration of the tumour which fully recovered following surgical decompression. Nine of the 15 patients presenting with visual impairment had improvement after treatment and the visual status remained stable in all others. One patient with acromegaly and one with a prolactinoma achieved normalization of elevated hormonal abnormality four and 10 months after SCRT, respectively. The remaining seven patients with a secretory adenoma had declining hormone levels at last follow-up. Newly initiated hormone replacement therapy was required in five patients. At a median follow-up of 9 months (range 1-44 months), the 1 and 2 year actuarial progression free and overall survival were 100%.

CONCLUSION

Stereotactic conformal radiotherapy is a high precision technique suitable for the treatment of pituitary adenomas requiring radiotherapy. Preliminary results suggest effective tumour control and low toxicity within the range expected for conventional external beam radiotherapy. While the technique is of potential benefit in reducing the volume of normal brain irradiated, the advantages in terms of sustained tumour control and reduced toxicity over conventional radiotherapy need to be demonstrated in long-term prospective studies.