RARE-31. Radiation induced malignancy associated with pediatric craniopharyngioma: a single institution experience

BACKGROUND: Therapy for pediatric craniopharyngioma, a rare suprasellar tumor, includes surgical resection with consideration for intracranial radiation. Radiation is associated with increased risk of secondary malignancies. Between 2000 and 2021, 81 pediatric patients with craniopharyngioma were treated at our institution; 3 of 54 (5.6%) who received radiation therapy(RT) developed secondary malignancy within the treatment field. CASE DESCRIPTIONS: In all 3 cases, initial imaging demonstrated cystic/solid suprasellar mass and underwent resection; pathology revealed calcifications and wet keratin consistent with craniopharyngioma. None had known cancer predispositions. The first patient (male), presented at 4-years-old with headaches. He underwent subtotal resection (STR) with cyst fenestration(w/CF) and received 55.8Gy photon 3D-Conformal RT. Six-years later, the tumor progressed (edge of RT field). Patient underwent a second STRw/CF and fractionated RT(50.4Gy). Both pathologies were consistent with(c/w) papillary craniopharyngioma. Eight-years from first RT, progression occurred again within the RTfield; pathology revealed an (adeno)squamous carcinoma. The second patient, a 5-year-old female, presented with vision loss, underwent partial resection and received 54Gy focal proton therapy for adamantinonatous craniopharyngioma. Almost 5-years later, an unresectable right basal ganglia/globus pallidus mass was noted in the 30-54Gy field. Pathology was c/w anaplastic astrocytoma(AA). The third, a 9-year-old female was treated with 54Gy photon radiation and 7 years later had evidence of increasing mass. Pathology revealed high-grade-diffuse-glioma(HGDG). Molecular analysis of AA/HGDG both revealed PDGFRA amplification and CDKN2A/B homozygous loss. DISCUSSION/CONCLUSION: Malignant CNS tumors are reported following radiotherapy for a variety of primary CNS lesions. While radiation is a valuable therapy in achieving long-term disease control of pediatric craniopharyngiomas, it is important to understand the risk of developing secondary malignant neoplasms. Our report adds to the body of literature describing secondary malignancies post radiation therapy for the treatment of pediatric craniopharyngioma.

LGG-64. A Phase II Study of Pegylated Interferon in Children with Recurrent or Refractory and Radiographically or Clinically Progressive Juvenile Pilocytic Astrocytomas and Optic Pathway Gliomas (NCT02343224)

Unresectable Juvenile Pilocytic Astrocytomas (JPA) and Optic Pathway gliomas (OPG) are chronic diseases that can have solid +/- cystic components. We wanted to evaluate the objective response to pegylated interferon Alpha2B in this group of patients in a prospective single arm Phase II clinical trial. Eligibility criteria: age 3 -25 years, patients with neurofibromatosis (NF) were eligible, evidence of measurable disease in MRI, no limitation in the number of prior therapies including chemotherapy and radiation. Exclusion criteria: prior pegylated interferon exposure, less than 2 years from radiation, active autoimmune disease. Subjects enrolled received pegylated interferon 1 mcg/kg/dose SQ weekly, to a max dose of 150mcg/dose in 28 day cycles for up to 2 years. The study design is a Simon two stage design. If no complete or partial responses among the first 9 patients, the study will terminate. Nine subjects enrolled: 4 females, 5 males, median age of 11years, 6 Caucasians, 3 African Americans. Two subjects with NF. Molecular findings KIAA-BRAF fusion (6), V600E mutation (1), CDK2A loss (1). Location: brain (7), brain and spine (2). We enrolled a heavily pre-treated population, patients with prior radiation ( 1), nine with prior chemotherapy, the average number of regimens 4 (range 2-6). No complete responses or partial responses were seen. Two patients with prolonged stable disease 75+months and 66+ months. At 12 and 24 month EFS 76.2% (95%CI52.1-100%). Median EFS has not been reached. The 12 and 24 months survival estimate 75% (95% CI 50.3-100%), median survival has not been reached. Side effects as expected mostly grade 1-2. No grade 4 event related to pegylated interferon were seen. This is the first report of pegylated interferon in OPG and JPA, two patients with prolonged stable disease suggesting that pegylated interferon can offer potential benefit in this population and additional studies are important.

RARE-28. The use of subcutaneous interferon in patients with craniopharyngioma: an institutional retrospective review

Current strategies for managing craniopharyngioma result in significant morbidity. Successful treatment with interferon alfa(INFα) after progression is reported in the literature. This retrospective review details our institutional experience with INFα in craniopharyngioma patients. Method: Between 2000-2021, we treated 81 craniopharyngioma patients. Twenty-two patients received 26 treatment courses of subcutaneous INFα. Twenty-three courses were evaluable for response. Results: Ten patients received upfront INFα after cyst decompression +/- ommaya placement. Progression free survival(PFS) ranged between 7-38mo. Three patients continue on treatment (10+, 12+, 14+mo); seven progressed (four on treatment (7, 9, 25, 38mo), three after treatment (13, 19, 32mo)). At progression, three underwent surgery alone, three underwent surgery and radiation, one resumed INFα. Thirteen patients received INFα after progression. Prior to INFα, eight patients had had surgery, five surgery and radiation. Two in each group had INFα, previously. PFS ranged between 5-82+mo. One patient remains on treatment (5+mo); four continue in follow-up without progression (23+,40+,64+,82+mo) with two patients avoiding radiation to date; eight progressed (three on treatment (6-8mo), five after treatment (16,24,26,46,71mo)). At progression, two underwent surgery alone, three underwent surgery and radiation, one received re-irradiation, two resumed INFα. While receiving INFα, two patients experienced serious adverse events (one intra-tumoral hemorrhage (not attributed to INFα), one suicidal ideation). Both recovered. One tolerated retreatment with INFα. Three additional patients stopped INFα for intolerance, but two received INFα at subsequent progression. No other unanticipated side effects were reported. Conclusion: INFα therapy in patients with both newly diagnosed and progressive craniopharyngioma delayed the need for aggressive surgical resection and/or radiotherapy in some cases. In some patients, INFα resulted in prolonged stabilization of disease delaying or avoiding radiation. Overall, INFα side effects were manageable. These results are encouraging regarding INFα therapy for patients with craniopharyngioma and warrant further evaluation with a clinical trial.

Impact of executive functioning on health-related quality of life of pediatric brain tumor survivors

BACKGROUND

Brain tumor survivors are at risk for significant late effects following treatment completion that may adversely impact health-related quality of life (HRQOL). The current study examines the relationship between executive functioning (EF) and HRQOL in pediatric brain tumor survivors within a longitudinal framework. We hypothesized that early deficits in EF would be related to less optimal HRQOL in this population.

PROCEDURE

The current study utilized retrospective medical chart review to identify neurocognitive correlates of HRQOL in 137 youth previously treated for a pediatric brain tumor. Participants completed the Pediatric Quality of Life Inventory (PedsQL) and neuropsychological assessment, including a well-validated measure of executive functioning (Behavior Rating Inventory of Executive Function; BRIEF). General linear regression and multivariate models were utilized to examine the relationship between child executive functioning and HRQOL.

RESULTS

Multiple domains of child executive functioning, as reported by parents on the BRIEF, significantly predicted parent-proxy reported HRQOL after controlling for demographic and medical covariates, including child intellectual functioning (IF). Similarly, after controlling for covariates, the BRIEF Cognitive Regulation Index was a significant predictor of self-reported physical and school functioning domains of HRQOL.

CONCLUSION

Current data demonstrate EF is a significant predictor of HRQOL during survivorship for youth previously diagnosed with a pediatric brain tumor. Results suggest that opportunities may exist to intervene and improve HRQOL of pediatric brain tumor survivors by targeting EF.

MBCL-14. A STUDY OF LOW-DOSE CRANIOSPINAL RADIATION THERAPY IN PATIENTS WITH NEWLY DIAGNOSED AVERAGE-RISK MEDULLOBLASTOMA

INTRODUCTION

Medulloblastoma is one of the most common malignant brain tumors in children. To date, the treatment of average-risk (non-metastatic, completely resected) medulloblastoma includes craniospinal radiation therapy and adjuvant chemotherapy. Modern treatment modalities and now risk stratification of subgroups have extended the survival of these patients, exposing the long-term morbidities associated with radiation therapy.

METHODS

We performed a single-arm, multi-institution study, seeking to reduce the late effects of treatment in patients with average-risk medulloblastoma prior to advances in molecular subgrouping. To do so, we reduced the dose of craniospinal irradiation by 25% to 18 gray with the goal of maintaining the therapeutic efficacy as described in CCG 9892 with maintenance chemotherapy.

RESULTS

28 patients aged 3–30 years were enrolled across three institutions between April 2001 and December 2010. Median age at enrollment was 9 years with a median follow-up time of 11.7 years. The 3-year relapse-free (RFS) and overall survival (OS) were 78.6% (95% CI 58.4% to 89.8%) and 92.9% (95% CI 74.4% to 98.2%), respectively. The 5-year RFS and OS were 71.4% (95% CI 50.1% to 84.6%) and 85.7% (95% CI 66.3% to 94.4%), respectively. Toxicities were similar to those seen in other studies; there were no grade 5 toxicities.

CONCLUSIONS

Given the known neurocognitive adverse effects associated with cranial radiation therapy, studies to evaluate the feasibility of dose reduction are needed. In this study, we demonstrate that select patients with average-risk medulloblastoma may benefit from reduced craniospinal radiation dose of 18 gray without impacting relapse-free or overall survival.

MBCL-15. IMPACT OF MOLECULAR SUBGROUPS ON OUTCOMES FOLLOWING RADIATION TREATMENT RANDOMIZATIONS FOR AVERAGE RISK MEDULLOBLASTOMA: A PLANNED ANALYSIS OF CHILDREN’S ONCOLOGY GROUP (COG) ACNS0331

The COG conducted a randomized trial for average-risk medulloblastoma (AR-MB). Patients age 3–21 years were randomized to a radiation boost to the whole posterior fossa (PFRT) or an involved field volume (IFRT) after receiving CSI. Patients age 3–7 years were also randomized to standard dose CSI (23.4Gy, SDCSI) or low dose CSI (18Gy, LDCSI). 464 evaluable patients were available to compare PFRT vs. IFRT and 226 for SDCSI vs. LDCSI. 380 cases had sufficient tissue for DNA methylation-based molecular classification: 362 confirmed medulloblastoma; 6 non-medulloblastoma; 12 inconclusive. Molecular subgrouping confirmed the following representation amongst the evaluable cohort: 156 Group 4 (43.1%), 76 Group 3 (21.0%), 66 SHH (18.2%), 64 WNT (17.7%). Five-year event-free survival (EFS) estimates were 82.5±2.7% and 80.5±2.7% for IFRT and PFRT, respectively (p=0.44). Five-year EFS estimates were 71.4±4.4% and 82.9±3.7% for LDCSI and SDCSI, respectively (p=0.028). EFS distributions differed significantly by subgroup (p<0.0001). Group 3 had the worst outcome, while WNT had the best outcome. There was a significant difference in EFS by RT group among SHH patients; SHH patients receiving IFRT arm had better EFS compared to PFRT (p=0.018). There was a significant difference in EFS distributions by CSI group in Group 4 patients; young Group 4 patients treated with SDCSI had better EFS compared to LDCSI (p=0.047). As previously reported, IFRT is noninferior to PFRT in all patients with AR-MB but LDCSI is worse than SDCSI in younger children. Significant differences in outcome by study randomization and molecular subgroup are observed.

Successful treatment of a child with a prolactin secreting macroadenoma with temozolomide

Prolactinomas are a rare subset of brain tumors in pediatrics. We report a child with a prolactin secreting macroadenoma which was refractory to initial treatment with a dopamine antagonist. Given the location of her tumor she was ineligible for surgical resection. Temozolomide (200 mg/m2×5 days each month) was administered with a dramatic and prolonged response in tumor size, prolactin level, and symptoms, with no side effects from treatment. We demonstrate the benefit of temozolomide in the treatment of a pediatric patient with prolactinoma.

Successful Retreatment of a Child with a Refractory Brainstem Ganglioglioma with Vemurafenib

A child with brainstem ganglioglioma underwent subtotal resection and focal radiation. Magnetic resonance imaging confirmed tumor progression 6 months later. Another partial resection revealed viable BRAF V600E-positive residual tumor. Vemurafenib (660 mg/m(2) /dose) was administered twice daily, resulting in >70% tumor reduction with sustained clinical improvement for 1 year. Vemurafenib was then terminated, but significant tumor progression occurred 3 months later. Vemurafenib was restarted, resulting in partial response. Toxicities included Grade I pruritus and Grade II rash. Vemurafenib was effectively crushed and administered in solution via nasogastric tube. We demonstrate benefit from restarting vemurafenib therapy.

Intensive multimodality treatment for children with newly diagnosed CNS atypical teratoid rhabdoid tumor

PURPOSE

Atypical teratoid rhabdoid tumor (ATRT) of the CNS is a highly malignant neoplasm primarily affecting young children, with a historic median survival ranging from 6 to 11 months. Based on a previous pilot series, a prospective multi-institutional trial was conducted for patients with newly diagnosed CNS ATRT.

PATIENTS AND METHODS

Treatment was divided into five phases: preirradiation, chemoradiation, consolidation, maintenance, and continuation therapy. Intrathecal chemotherapy was administered, alternating intralumbar and intraventricular routes. Radiation therapy (RT) was prescribed, either focal (54 Gy) or craniospinal (36 Gy, plus primary boost), depending on age and extent of disease at diagnosis.

RESULTS

Between 2004 and 2006, 25 patients were enrolled; 20 were eligible for evaluation. Median age at diagnosis was 26 months (range, 2.4 months to 19.5 years). Gross total resection of the primary tumor was achieved in 11 patients. Fourteen patients had M0 disease at diagnosis, one patient had M2 disease, and five patients had M3 disease. Fifteen patients received radiation therapy: 11 focal and four craniospinal. Significant toxicities, in addition to the expected, included radiation recall (n = 2) and transverse myelitis (n = 1). There was one toxic death. Of the 12 patients who were assessable for chemotherapeutic response (pre-RT), the objective response rate was 58%. The objective response rate observed after RT was 38%. The 2-year progression-free and overall survival rates are 53% +/- 13% and 70% +/- 10%, respectively. Median overall survival has not yet been reached.

CONCLUSION

This intensive multimodality regimen has resulted in a significant improvement in time to progression and overall survival for patients with this previously poor-prognosis tumor.

Congenital glioblastoma: a clinicopathologic and genetic analysis

Congenital central nervous system (CNS) tumors are uncommon, accounting for 1% of all childhood brain tumors. They present clinically either at birth or within the first 3 months. Glioblastoma (GBM) only rarely occurs congenitally and has not been fully characterized. We examined clinicopathologic features and genetic alterations of six congenital GBMs. Tumors were seen by neuroimaging as large, complex cerebral hemispheric masses. All showed classic GBM histopathology, including diffuse infiltration, dense cellularity, GFAP-positivity, high mitotic activity, endothelial proliferation and pseudopalisading necrosis. Neurosurgical procedures and adjuvant therapies varied. Survivals ranged from 4 days to 7.5 years; two of the three long-term survivors received chemotherapy, whereas the three short-term survivors did not. Paraffin-embedded tissue sections were used for FISH analysis of EGFR, chromosomes 9p21 (p16/CDKN2A) and 10q ( PTEN/DMBT1); sequencing of PTEN and TP53; and immunohistochemistry for EGFR and p53. We uncovered 10q deletions in two cases. No EGFR amplifications, 9p21 deletions, or mutations of TP53 or PTEN were noted; however, nuclear p53 immunoreactivity was strong in 5/6 cases. Tumors were either minimally immunoreactive (n = 3) or negative (n = 3) for EGFR. We conclude that congenital GBMs show highly variable survivals. They are genetically distinct from their adult counterparts and show a low frequency of known genetic alterations. Nonetheless, the strong nuclear expression of p53 in these and other pediatric GBMs could indicate that p53 dysregulation is important to tumorigenesis.

Adult heights attained by children with hypothalamic/chiasmatic glioma treated with growth hormone

Hypothalamic/chiasmatic gliomas (H/CG) in children are commonly accompanied by endocrine dysfunction due to mass effects of the tumor itself or as a consequence of tumor therapy, with GH deficiency (GHD) being the most common disorder. We report the height outcomes of GH-treated H/CG patients with GHD. We reviewed the records of 14 GHD patients with H/CG who were treated with human GH. A comparison group of non-GH-treated H/CG patients was also identified. Heights were expressed as sd scores (SDS). For GH-treated patients, the mean initial height was -0.7 +/- 0.3 (+/-se). Their mean final height was -0.3 +/- 0.3. The mean change in height SDS for the GH-treated group was +0.4. The mean initial and final height SDS for the non-GHD patients were 0.6 (se = 0.4) and 0.0 (se = 0.4), respectively. The mean change in height SDS was -0.6. The GHD patients had significantly lower initial height SDS compared with the non-GHD patients (P = 0.01) and had a significantly greater change in their height SDS (P = 0.04). GH treatment for H/CG patients restores much of their growth potential and improves adult height to within normal limits.

Central nervous system atypical teratoid/rhabdoid tumor: results of therapy in children enrolled in a registry

PURPOSE

Atypical teratoid/rhabdoid tumor (AT/RT) of the CNS is an extremely rare and aggressive tumor of early childhood. The poor outcome with conventional infant brain tumor therapy has resulted in a lack of clear treatment guidelines. A registry has been established to create an outcomes database and to facilitate biology studies for this tumor.

MATERIALS AND METHODS

A standardized data sheet was provided to treating physicians listing the reports that were to be sent to the registry for abstraction. Follow-up information was sought twice yearly.

RESULTS

Information was complete for 42 patients. Median age at diagnosis was 24 months. Nine patients (21%) had disseminated disease at diagnosis. Sixteen tumors were infratentorial; 26 were supratentorial. Twenty patients (48%) received a primary complete resection. Primary therapy included chemotherapy in all patients, radiotherapy in 13 patients (31%), stem-cell rescue in 13 patients (31%), and intrathecal chemotherapy in 16 patients (38%). Recurrent or progressive disease was reported in nine and 19 patients, respectively. Twenty-seven patients (64%) are dead of disease (3 to 62 months from diagnosis) and one patient died of toxicity. Fourteen patients (33%) show no evidence of disease (9.5 to 96 months from diagnosis). The median survival is 16.75 months and the median event-free survival is 10 months.

CONCLUSION

Aggressive therapy has prolonged the natural history in a subset of children. Prospective multi-institutional and national clinical trials designed specifically for AT/RT are needed. Enrollment onto the AT/RT registry should be continued.

Endocrine outcome in children with medulloblastoma treated with 18 Gy of craniospinal radiation therapy

Craniospinal radiation therapy (CSRT) combined with chemotherapy results in significant endocrine morbidity. Between 1987 and 1990, a trial using 18 Gy was conducted to treat 10 young children with medulloblastoma. There were 7 survivors. We compared the endocrine outcome in these children (group 18 Gy) to that of a comparable group treated with conventional doses of CSRT that ranged from 23 to 39 Gy (group CD). Both groups had an identical history of chemotherapy and tumor stage and were treated with recombinant growth hormone therapy (rhGH). The mean age of group 18 Gy at diagnosis was 4.0 years, and rhGH treatment was initiated in 6 children at age 9.2 years. Group CD (12 children) was diagnosed at a mean age of 5.8 years and rhGH started in 11 children at a mean age of 9.6 years. The dose of rhGH used in both groups was identical (0.3 mg/kg/wk). For group 18 Gy, adult heights and sitting heights (a mean standard deviation score of -1.01 +/- 1.11 and -1.62 +/- 1.16, respectively) were statistically greater (P < 0.05) than those for group CD (mean standard deviation score of -2.04 +/- 0.83 and -3.16 +/- 1.43, respectively). Moreover, adult heights of group 18 Gy were not different from midparental heights, unlike group CD, whose adult heights were less than midparental heights (P < 0.0001). Of other endocrine sequelae, 10 patients of the CD group were hypothyroid, 3 had adrenal insufficiency, 3 had hypogonadism, and 2 had early puberty. In contrast, within group 18 Gy, only 1 was hypothyroid (P = 0.006) and 1 had early puberty. We conclude that endocrine morbidity was significantly reduced with 18 Gy CSRT in young children with medulloblastoma.

Optic radiation involvement in optic pathway gliomas in neurofibromatosis

PURPOSE

Optic pathway gliomas (pilocytic astrocytomas) in neurofibromatosis type 1 (NF-1) typically involve some combination of the optic nerves, chiasm, or optic tracts. Involvement of the optic radiations is rare.

DESIGN

This paper describes seven patients with NF-1 with gliomas involving the pregeniculate optic pathway in addition to the optic radiations.

METHODS

A retrospective database review was made of all patients with NF-1 and optic pathway gliomas seen by one of the authors (G.T.L.) at the Children's Hospital of Philadelphia from July 1993 to October 2001. Patients with involvement of pregeniculate optic pathway and the optic radiations were identified. From November 2001 to February 2003, patients were sought prospectively. Cases were also identified from the practice of another author (M.C.B.) at Arkansas Children's Hospital.

RESULTS

Four patients from Children's Hospital of Philadelphia (three of 83 total NF-1/optic pathway gliomas from July 1993 to October 2001 and one prospectively) and three from Arkansas Children's Hospital were identified. Two had expanding mass lesions within the white matter of the temporal or parietal lobes, which were histopathologically demonstrated to be pilocytic astrocytomas. The other five had radiographic involvement of the optic radiations but did not undergo biopsy. In three of the cases the vision was 20/200 or worse in each eye.

CONCLUSIONS

Optic pathway gliomas in NF-1 may rarely involve the optic radiations. Optic radiation involvement may signal a more aggressive optic pathway glioma in patients with neurofibromatosis-1.

Craniospinal radiation in the treatment of biopsy-proven intracranial germinomas: twenty-five years' experience in a single center

PURPOSE

The optimal treatment for intracranial germinomas remains controversial. We report on our 25-year experience using craniospinal irradiation (CSI) for this disease.

METHODS AND MATERIALS

Between September 1976 and May 2001, 39 patients with biopsy-proven intracranial germinomas seen at the Children's Hospital of Philadelphia/Hospital of the University of Pennsylvania received CSI. Thirteen of 36 patients (36%) had evidence of spinal dissemination. Median doses to the whole brain, primary site, and spine were 36 Gy (range, 18-44.2 Gy), 50.4 Gy (range, 44-55.8 Gy), and 30.6 Gy (range, 18-40 Gy), respectively.

RESULTS

With a median follow-up of 7.1 years (range: 1.5-20.2 years), there have been no documented relapses. This includes 5 patients without spinal dissemination who received 18-19.8 Gy to the craniospinal axis; for these patients, the median length of follow-up was 5.5 years (range, 1.3-6.8 years). One patient, who had no evidence of disease 12.9 years after CSI, died of unknown causes 4 months later.

CONCLUSIONS

Our treatment of intracranial germinomas with CSI has yielded outstanding results with no known relapses during a long follow-up period. These results must be considered when evaluating other approaches, such as chemotherapy only or local field irradiation.

Adult height and adult sitting height in childhood medulloblastoma survivors

Outcome in adult height and sitting height is poor in children surviving medulloblastoma due to craniospinal irradiation (CSRT) and chemotherapy. We evaluated adult height and sitting height in 51 medulloblastoma patients stratified into four groups: G1, GH-deficient (GHD) patients treated with 23-39 Gy CSRT but not treated with GH [recombinant human (rh)GH]; G2, patients treated with rhGH; G3, patients who were not GHD; and G4, patients treated with 18 Gy CSRT and rhGH. Standing/sitting height of each group was compared with parental height and previously reported outcome studies. The rhGH dose was 0.3 mg/kg.wk, a higher dose compared with other reports of adult heights. The adult heights were significantly taller in group G2 [mean height SD score (SDS) = -1.86] than that achieved in previous studies (P < 0.0001), but not different from group G3, non-GHD (mean SDS = -1.55). The tallest stature achieved was in group G4 (18 Gy CSRT), a height SDS of -1.01. Sitting heights were significantly less than the normal population, with mean SDS of -2.96 but -1.62 in group G4. We conclude that adult heights but not sitting heights in medulloblastoma survivors are significantly improved with the higher dose of rhGH. The lower dose of CSRT further improves not only adult height but also sitting height.

Delayed cyclin B1 expression during the G2 arrest following DNA damage

Exposure of cells to DNA damaging agents results in a G2 arrest. Exposure of HeLa cells to camptothecin, etoposide or nitrogen mustard for 1 h in S phase resulted in delayed expression of cyclin B1 mRNA during the G2 arrest. Initially the levels of cyclin B1 protein were low as well; however, with extended time the cells blocked in G2 regained higher levels of cyclin B1 protein. In the case of cells treated with nitrogen mustard the higher levels coincided with cells exiting the G2 block into G1. However, with camptothecin or etoposide treatment, while the accumulation of cyclin B1 protein was delayed, its levels eventually surpassed peak levels seen in control cells, in spite of the fact that cells were still blocked in G2. These cells did not continue to progress through the cell cycle indicating further complexity to the mechanisms underlying the G2 block. Decreased transcription and stability of cyclin B1 mRNA were shown to occur after treatment with these DNA damaging agents. These results indicate that suppression of cyclin B1 mRNA expression is one consequence of DNA damage in HeLa cells.