Pineocytoma

PPTs comprise from 15% to 30% of all pineal region tumors, and pineocytomas make up about 30% to 60% of PPTs. The category of PPTs includes pineocytomas, mixed pineocytomas/pineoblastomas (PPTs of intermediate differentiation [PPTID]), and pineoblastomas. Pineocytomas are slow-growing tumors that arise from the parenchyma of the pineal gland and are classified as World Health Organization (WHO) grade II lesions. As is the case with many tumor types arising within the pineal region, pineocytomas are rare lesions and remain underrepresented in the literature in terms of receiving stereotactic radiosurgery.

A recent large retrospective study by Mori and colleagues examined the safety and efficacy of GKRS (KULA system, Elekta, Tokyo) as an adjuvant treatment on 49 patients with 74 tumors involving the pineal region over a 15-year period. Specifically, 9 patients presented with PPTs (19 tumors in total), and all PPTs were diagnosed by histologic confirmation. Furthermore, all PPT cases underwent surgical resection before GKRS, making the radiosurgical intervention in this study a postoperative, adjuvant modality. Thirteen total pineocytomas found in 6 patients were included in the study. The marginal dose of GKRS ranged from 12.5 to 20.3 Gy and the maximum dose ranged from 17 to 40 Gy ( Table 1 ); these doses include all PPTs and the investigators do not designate the radiation values for pineocytomas only. In addition, the local tumor control (LTC) rate at 3 and 5 years was 85%, and the progression-free survival (PFS) rate at 3 and 5 years was 80%. These were the highest LTC and PFS rates in the study, leading the investigators to conclude that GKRS is both safe and effective as an adjuvant treatment of pineocytomas.

Kano and colleagues simultaneously published their institutional experience with pineocytomas over a 20-year period. All PPTs in this study were histologically confirmed; 6 of the 20 patients studied had previous surgical resection, and of these 6 patients, 3 underwent previous fractionated radiation therapy, 3 received chemotherapy, and 2 received both. The investigators do not specify which histologic type underwent surgery initially and/or adjuvant therapy before the initiation of GKRS (Elekta Inc, Atlanta, GA, USA). This study included 13 patients with pineocytomas; the margin dose of GKRS ranged from 12 to 20 Gy, whereas the maximum dose ranged from 24 to 40 Gy (see Table 1 ). No instances of progressive disease were noted among the patients with pineocytoma; 3 patients experienced a complete response, 8 patients showed a partial response, and 2 patients had evidence of stable disease. The survival rates and PFS rates were also remarkably high in this patient group: actuarial 1-year, 3-year, and 5-year survival rates were 100%, 92.3%, and 92.3%, respectively. PFS rates were 100% at 1, 3, and 5 years. The conclusion drawn from this study regarding GKRS treatment of pineocytomas, therefore, was that stereotactic radiosurgery is both a safe and effective alternative to open surgical resection.

Lekovic and colleagues include 8 patients with pineocytoma in their retrospective analysis of GKRS (Leksell GammaPlan, Elekta, Tokyo) for pineal region tumors. All of these patients underwent biopsy leading to a tissue diagnosis before institution of GKRS. The peak dose ranged from 26 to 32 Gy. Among these 8 patients, half showed a partial response, whereas the other half showed no change in symptoms (see Table 1 ). Despite the high rates of tumor control that these investigators reported, they still concluded that craniotomy with an attempt at gross total resection (GTR) is the best treatment approach for benign tumors such as pineocytomas given that this is the closest guarantee to a definitive cure. However, the investigators did state that based on their data, GKRS has potential as a primary treatment modality for pineocytomas, especially in cases in which GTR is deemed impossible or achievable only at an unacceptable risk to the patient. In the final analysis, the Lekovic study supported surgery with an attempt at GTR over GKRS as the primary intervention, with GKRS reserved for treatment of residual or recurrent disease or in cases in which GTR comes at too high a cost. More recent literature supports this conclusion, namely a study by Clark and colleagues that examined the benefits of GTR versus subtotal resection (STR) combined with adjuvant radiation therapy. This study concluded that GTR leads to tumor control rates suggestive of a complete cure compared with STR and radiotherapy. Moreover, STR alone versus STR and radiotherapy showed no difference in tumor control rates, suggesting that postoperative adjuvant radiotherapy offers no advantage in the treatment of subtotally resected lesions. The investigators note in this review that the postoperative radiotherapy in their retrospective patient population is either fractionated radiotherapy or stereotactic radiosurgery, but there is no subgroup analysis involving the patients who received stereotactic radiosurgery. Therefore, it is difficult to extend these investigators’ conclusion to include all patients undergoing stereotactic radiosurgery, as well as those patients who undergo stereotactic radiosurgery as a primary treatment modality. Before this study, Deshmukh and colleagues arrived at a similar conclusion regarding pineocytomas, albeit within a smaller sample size (9 patients compared with 166 patients in the study by Clark and colleagues). Within this small sample, only 5 patients underwent GKRS, but all showed either LTC or reduction of tumor size. The investigators therefore concluded that radiosurgery seems to be effective for LTC, despite the small sample size and short follow-up period (19.3 months).

The retrospective study from Reyns and colleagues included 8 patients with pineocytomas; 6 of these patients were treated primarily with GKRS (Leksell Gamma Knife models B and C, Elekta, Tokyo), whereas the other 2 underwent GKRS after subtotal surgical resection. The central dose ranged from 24 to 40 Gy. Of the 6 patients undergoing GKRS as a primary intervention, 1 patient showed complete regression, 3 patients showed partial regression of at least 50%, and 2 patients had no change in the size of the tumor (see Table 1 ). Of the 2 patients who underwent GKRS after STR, one was lost to follow-up, whereas the other patient showed partial regression. The investigators conclude from these data that GKRS is an effective primary treatment modality in the case of pineocytomas and can serve as the sole means of intervention in such patients.

Pineoblastoma

Pineoblastomas are highly malignant parenchymal tumors of the pineal region that account for approximately 4% of PPTs and are classified as WHO Grade IV lesions. These tumors realize their malignant potential in the form of CSF seeding (14%–43% of cases) as well as extracranial metastases (most commonly bone). Mean survival time after multimodal intervention (surgery, chemotherapy, radiation) is typically around 2 years; overall 5-year survival ranges from 10% to 51%, and without treatment survival may be only a few months. Similar to their benign PPT counterpart, the pineocytoma, pineoblastomas are exceedingly rare lesions and there is limited experience treating these lesions with stereotactic radiosurgery.

Mori and colleagues include only 4 pineoblastomas (2 patients) in their large retrospective study of 49 patients, illustrating the scarcity of this tumor type. As noted earlier, the study combined pineoblastomas, pineocytomas, and PPTIDs (referred to as mixed pineocytoma/pineoblastoma in this article) in their GKRS dose planning data, so the 4 pineoblastomas fall within the treatment ranges mentioned earlier. Given that there was only 1 patient with a PPTID, the investigators combined this patient with the 4 pineoblastomas in the data analysis. Significantly, the LTC rate for this group was only 30% at 2 years, whereas the PFS rate at 2 years was 33% ( Table 2 ). There was a statistically significant difference in LTC between the pineocytoma group and the pineoblastoma/PPTID group, while the difference in PFS approached statistical significance. Both pineoblastoma patients in this study had evidence of tumor progression at 3 and 13 months after GKRS. Based on these data, especially because the pineoblastomas both relapsed, the investigators do not recommend GKRS as an adjuvant therapy in the management of pineoblastoma.

Of the 20 patients with PPT analyzed in the Kano and colleagues study, 5 patients had pineoblastomas and 2 patients had mixed tumors (PPTID). The GKRS dosing plan mentioned earlier in the setting of the pineocytomas reported in this study includes the pineoblastomas and PPTIDs as well. Based on follow-up imaging, there were 2 pineoblastomas with complete tumor resolution, 1 tumor had tumor regression, and 1 tumor was unchanged. However, in 2 patients with pineoblastomas, tumor progression was noted at 12.8 and 31.2 months, leading to repeat GKRS in one of these patients. The actuarial survival rates and PFS rates were significantly lower in the patients with pineoblastoma compared with those with pineocytoma, in keeping with previous studies (see Table 2 ). In terms of overall survival, the 1-year, 3-year, and 5-year rates were 95%, 80%, and 68.6%, respectively. These numbers compare favorably with those quoted in the Schild and colleagues study, in which patients underwent various treatments, leading the investigators to suggest that adjuvant GKRS as part of an aggressive oncologic intervention may improve outcomes for pineoblastomas. This finding prompted the investigators to conclude that GKRS can prove an important adjunct in the multimodal treatment of pineoblastomas.

One patient with pineoblastoma is included in the Lekovic and colleagues study, with histologic confirmation coming from open biopsy. The maximum dose to this tumor was 28 Gy, and there was no change in tumor size on follow-up imaging at 45 months after GKRS (see Table 2 ). This was the second largest tumor of the 17 tumors included in the study (23.0 cm ³ ). The investigators used GKRS as adjuvant therapy in this pineoblastoma, but it is unclear whether it was the sole adjuvant treatment or combined with conventional external beam radiation therapy (EBRT)/intensity modulated radiation therapy. Given that these investigators had only 1 pineoblastoma in their series, they understandably refrain from drawing any conclusions about the role of GKRS in its management.

The study by Reyns and colleagues included a total of 5 pineoblastomas, most of which were subjected to different management protocols. GKRS was the initial intervention in 1 case of pineoblastoma; it followed STR in 1 case; it was instituted before chemotherapy in 1 case of recurrent pineoblastoma that was initially treated with surgery and radiation; and in another 2 cases, GKRS was performed as a sandwich protocol between 2 chemotherapy sessions. The maximum dose ranged from 28 to 50 Gy; complete regression was observed in 2 patients, complete regression but with brain metastasis in 1 patient, partial regression (90%) in 1 patient, and progression in 1 patient (see Table 2 ). The patient with progression died 36 months after GKRS as a result of tumor size progression, whereas the patient with partial regression of 90% died 20 months after GKRS from carcinomatous meningitis. Based on these limited data, the investigators conclude that the combination of GKRS with chemotherapy is an effective management strategy to induce LTC. However, they cannot faithfully conclude that GKRS confers any control over leptomeningeal spread, and they state that aggressive chemotherapy and/or craniospinal irradiation are critical in reducing the risk of distant metastasis.

The fundamental conclusion from these studies is that GKRS alone seems ineffective in treating pineoblastomas but that in combination with adjuvant treatments it has shown potential for controlling local tumor growth and possibly improving overall survival. An early study by Manera and colleagues is essentially the only such study that found stereotactic radiosurgery alone (LINAC radiosurgery, not GKRS, Leksell Gamma Knife model B [Elekta]) to be effective in treating pineoblastomas, albeit in 2 patients. Thus, the question remains as to the exact role of GKRS in the multimodal treatment of pineoblastomas: is it a substitute for conventional EBRT or simply an additional tool in the armamentarium of the neuro-oncologist?