1. Introduction

Granulosa cell tumors (GCTs) result from neoplastic transformation of the ovarian sex-cords. These are rare tumors, comprising 2–5% of all ovarian malignancies, but represent 70% of malignant sex cord-stromal tumors [1]. There are two histologically distinct subtypes: adult-type GCTs, which tend to occur after the third decade of life, and juvenile-type GCTs, which tend to occur in children and young adults [2]. Adult-type GCTs are low-grade malignancies and generally remain localized. Most patients will present with symptoms such as abnormal vaginal bleeding related to GCT-based estrogen production, or bulk symptoms due to GCT size. Given these factors, GCTs are often diagnosed early, with the vast majority of patients presenting with Stage I disease [1, 2]. Standard treatment is primary surgery, which is often curative for early-stage disease [3]. However, these tumors tend to have late and multiple recurrences, likely due to persistent occult disease with an indolent growth rate. Reported recurrence rates are 20% for Stage IA and up to 48% for Stage II–IV disease; the median time to recurrence is 4–6 years, though longer recurrences intervals are reported, with a 20-year survival rate of 67% [3].

Advanced and recurrent GCTs present a considerable clinical challenge with limited viable treatment options and no established optimal management strategy. In fact, there are currently no Food and Drug Administration (FDA) approved therapies for the treatment of recurrent GCTs. A major challenge is the indolent nature of these tumors, resulting in limited response to standard therapies including chemotherapy and radiation. Upwards of 70% of women who experience recurrence succumb to this disease [4]. For appropriate patients, surgical resection of recurrent disease is often offered given the indolent growth pattern and long disease-free intervals. For patients with unresectable tumors, platinum-based combination chemotherapy regimens have been explored with variability in reported response rates [5]. Given the toxicity associated with these treatments and variable benefit, alternative treatment strategies are needed to improve survival and optimize quality of life.

Hormonal therapy has also been explored as a systemic treatment option, as GCTs generally express steroid hormone receptors. Hormonal therapy for GCTs was recently evaluated in the PARAGON trial, a basket trial that included seven phase 2 trials assessing the efficacy of anastrozole in targeting estrogen receptor (ER) or progesterone receptor (PR) positive recurrent/metastatic gynecological malignancies. Among the 38 patients with GCTs in this trial, the clinical benefit rate at 12 weeks was 78.9%, with one partial response and 76.3% with stable disease. Median progression free survival (PFS) was 8.6 months, and the treatment was generally well-tolerated with the most common reported side effects being grade 1 fatigue or hot flashes (50% each) and arthralgia (47.5%) [6]. The phase II ALEPRO trial, is currently recruiting to evaluate abemaciclib and letrozole in rare recurrent estrogen receptor positive (ER+) ovarian tumors including adult-type ovarian GCTs, though reporting of these study results are still pending [7].

In hormone receptor (HR) positive breast cancer, cyclin dependent kinase 4/6 (CDK4/6) inhibitors along with hormonal therapy has been associated with significant improvement in PFS [8]. CDK4/6 inhibitors are now being studied in gynecological cancers. In a phase II trial including patients with recurrent low-grade serous ovarian cancer, treatment with CDK4/6 inhibition led to clinical benefit in 79% of patients [9]. Another phase II trial showed improvement of PFS in advanced or recurrent endometrial cancer patients when treated with letrozole and palbociclib compared to letrozole alone (median 8.3 vs. 3.1 months) [10].

In tumor profiling of adult GCTs with the forkhead box L2 (FOXL2) c.C402G mutation, a reported alteration is loss of cyclin-dependent kinase inhibitor 2A (CDKN2A) [11], encoding p16, which normally inhibits CDK4/6 protein function. Considering the molecular profile of GCTs coupled with increased estrogen production [12], there may be a benefit to the addition of CDK4/6 inhibitors to estrogen blockade in patients with granulosa cell tumors. Mechanisms by which this benefit may be derived are shown in Fig. 1 (Ref. [12, 13, 14]).

Fig. 1.Potential mechanisms of action of estrogen blockade combined with CDK4/6 inhibition in granulosa cell tumors [12, 13, 14]. In HR+ tumor cells, estrogen receptors are activated by estrogen binding leading to the upregulation of Cyclin D expression, which binds to and activates CDK4/6. Activated CDK4/6 phosphorylates retinoblastoma (RB) protein releaseing the E2F transcription factor, resulting in cell cycle progression from G1 to S phase, promoting cell growth and proliferation. Hormonal therapies (e.g., Fulvestrant) are antagonists to estrogen receptors. They bind to and block estrogen receptors, inducing receptor degradation and inhibition of downstream proliferative signaling. Aromatase inhibitors block the activity of the enzyme aromatase, which converts androgens (e.g., testosterone) into estrogen decreasing peripheral levels of estrogen, hence reducing signaling through the estrogen receptor pathway. Created with Biorender.com. CDK4/6: Cyclin Dependent Kinase 4/6; RB: retinoblasoma; ERE: Estrogen response element; E2F: Early region 2 binding factor.

The rarity of GCTs makes alternative therapies difficult to evaluate in large prospective trials. We report a case series of four patients with recurrent granulosa cell tumors who were treated with a combination of CDK4/6 inhibition and hormonal therapy.

2. Methods

Following institutional review board (IRB) approval (UCLA: IRB#22-0409), we performed a retrospective chart review at the University of California, Los Angeles (UCLA) Ronald Regan Medical Center to identify patients diagnosed with recurrent ovarian GCTs treated with CDK4/6 inhibitors in combination with hormonal therapy. Patients were identified and selected for inclusion in this case review by their treating oncologists based on diagnosis and prior treatment history. All patients were started on this combination therapy after having progressed through prior lines of hormonal therapy, and/or chemotherapy with or without radiation. Patient demographics, tumor characteristics, surgical data, adjuvant treatment information, radiological findings and treatment outcomes were collected from the electronic medical records. Treatment response was evaluated using serial radiological imaging and tumor response was assessed using Response Evaluation Criteria in Solid Tumors (RECIST). Duration of response was determined based on the CDK4/6 and hormonal therapy combination treatment start date to the time of progression. If disease did not progress, duration of reponse was determined based on the combination treatment start date to the date of the patient’s most recent imaging showing no evidence of disease (NED). Genomic tumor status was confirmed from commercial clinical grade next-generation sequencing methods performed for molecular tumor testing. Immunohistochemical (IHC) tumor status was derived from pathology reports using the tumor specimen evaluated closest to the start of this combination therapy.

3. Case report

Four patients diagnosed with recurrent ovarian GCTs were treated with a combination of CDK4/6 inhibitor and estrogen blockade. Table 1 outlines demographic information, clinical background and tumor characterization for each patient. All patients were diagnosed with adult-type ovarian GCTs and experienced multiple recurrences or disease progressions prior to the combination therapy. The median age at initial diagnosis was 42.5 years (range 27 to 73 years). Patients were all heavily pre-treated, experiencing a median of five recurrences or progressions (range 4–8) prior to receiving the combination therapy. Patients had a median of one prior line of chemotherapy and a median of 2.5 prior lines of hormonal therapy. Patients had a median of 4.5 prior surgeries (range 3–9), and two patients had previously been treated with radiation. All tumor samples had somatic FOXL2 and Telomerase reverse transcriptase (TERT) alterations on next-generation sequencing for genomic tumor testing. All tumors were hormone receptor positive by IHC tumor testing.

An overview of all patients’ combination therapy course and responses are outlined in Table 2. All patients were treated with palbociclib as the CDK4/6 inhibitor and concurrent estrogen blockade in their treatment. Three out of four patients derived clinical benefit seen through a durable duration of response from this therapy. One patient (Patient 1) had a complete response with a duration of 45 months and continues on this treatment at the time of this case report. One patient had partial response for a duration of 45 months (Patient 3), and another had stable disease for a duration of 14 months (Patient 4) prior to experiencing disease progression. Lastly, one patient (Patient 2) progressed on this therapy. Patients were monitored by their treating oncologists with regular visits to assess treatment response and evaluate for adverse effects. The therapy was overall well-tolerated, and no patient discontinued the treatment due to toxicity. There have been no reported significant side effects in patients who have continued treatment long-term.

Patient 1 underwent a robotic-assisted hysterectomy and was incidentally found to have an ovarian tumor, which pathology confirmed as a Stage IA adult GCT. After 2.7 years, imaging revealed a pelvic lesion, which was surgically resected and confirmed to be recurrent disease by pathology. The patient was treated with letrozole and had another recurrence within a year, prompting additional surgery. She was then treated with a combination of chemotherapy and fulvestrant. While on treatment, she was found to have oligometastatic recurrent disease of the pelvic sidewall. Following completion of chemotherapy, she was treated with stereotactic body radiation therapy at the site of this recurrence, and within two weeks, was started on the combination therapy of palbociclib with fulvestrant. Based off the most recent imaging, this patient’s duration of response was 45 months. The patient was on this treatment for 52 months and showed a remarkable durable response shown through imaging in Fig. 2.

Fig. 2.Imaging response to treatment (combination of local radiation and CDK4/6 inhibitor with fulvestrant) in Patient 1 on serial positron emission tomography/computed tomography (PET/CT) scans. (A) Baseline (prior to treatment): Enlarged lymph node is present in the left pelvic side wall (arrow). (B) First scan at three months post treatment: interval decrease in size of lymph node (now 5 mm) in the left pelvic side wall (arrow). (C) 17-month follow up: Interval decrease in size of lymph node (now non measurable) with focal calcification in the left pelvic side wall (arrow). (D) Four-year follow up: Stable non measurable lymph node with focal calcification in the left pelvic side wall (arrow).

Patient 2 initially presented with an adnexal mass and underwent surgery, with final pathology confirming Stage IIC adult GCT. After receiving adjuvant chemotherapy, the patient experienced several recurrences and was treated with various hormonal therapies including megace, anastrozole, letrozole, fulvestrant and tamoxifen. Ultimately, due to progression of disease, the patient was treated with a combination of palbociclib and letrozole for a period of seven months. This patient did not respond to the combination treatment and due to disease progression on therapy, the treatment was ultimately discontinued. Magnetic resonance imaging (MRI) imaging taken before the start of combination therapy and imaging taken at the time of progression can be seen in Fig. 3.

Fig. 3.Patient 2 MRI scans. (A) Baseline T1 post contrast MRI shows peritoneal nodule (arrow). (B) Follow up T1 post contrast MRI at seven months shows progression of disease with growth of peritoneal nodule (arrow).

Patient 3 underwent surgery for resection of an adult granulosa cell tumor. She was subsequently diagnosed with recurrence on two separate occasions which required surgery followed by hormonal therapy with an aromatase inhibitor (AI). She presented with recurrent disease involving the stomach, necessitating additional surgical intervention followed by continuation of AI therapy. Due to progression of disease in the liver, she was also treated with radiation before transitioning to endocrine therapy with fulvestrant. Progression of disease was documented after a few short months, at which point she was started on a combination of palbociclib with anastrozole. Follow-up imaging documented regression of disease. While on this treatment, she also received radiation. Due to a concern for gastric perforation coupled with progression of disease, she underwent another surgery and then was continued on palbociclib with anastrozole for an additional eight months. After an approximately 45 month duration of response, she ultimately progressed on this treatment, which was then discontinued. Representative imaging during the course of therapy is shown in Fig. 4.

Fig. 4.Patient 3 MRI scans. (A) Baseline T1 post contrast MRI shows left perirenal mass (arrow). (B) Follow up T1 post contrast MRI at 24 months shows partial response with decrease size of perirenal mass (arrow). (C) Follow up T1 post contrast MRI at 46 months shows progressive disease with development of new cystic mass (arrow).

Patient 4 initially underwent surgery followed by platinum-based chemotherapy. Her first recurrence occurred within 15 months, necessitating additional surgery. Within five months, the patient was diagnosed with another recurrence and underwent tumor debulking followed by hormonal therapy with AIs. She subsequently experienced several recurrences over the next 11 years which were treated with surgical intervention, chemotherapy and hormonal therapies including letrozole, anastrozole, megace and fulvestrant. After her last surgery, the patient began treatment with palbociclib paired with anastrozole, which was later switched to letrozole. The patient had stable disease with an approximately 14 month duration of response on this regimen before progressing. Imaging during the course of therapy is shown in Fig. 5.

Fig. 5.Patient 4 MRI scans. (A) Baseline T1 post contrast MRI shows left splenic hilum mass (arrow). (B) Follow up T1 post contrast MRI at 4 months shows stable splenic hilum mass (arrow). (C) Follow up T1 post contrast MRI at 15 months shows progressive disease with increase size of splenic hilum mass (arrow).

4. Discussion

In this series of heavily pre-treated patients with recurrent ovarian granulosa cell tumors, combination treatment with a CDK4/6 inhibitor and estrogen blockage provided clinical benefit as observed by durable responses in three out of four patients treated at our institution. Importantly, all patients had failed prior endocrine therapy. Treatment was very well-tolerated and no adverse events resulting from this treatment course were noted based on clinical evaluation. CDK4/6 inhibitor treatment is oral, which may provide benefit in terms of quality of life for patients in comparison to cytotoxic chemotherapy regimens. While not widely evaluated in GCTs, concurrent treatment with CDK4/6 inhibitors and hormonal therapies have shown benefits to patient quality of life, increased tolerability and reduced toxicity in breast cancer patients [15]. Given the oral administration, these treatments can be self-administered rather than requiring frequent hospital visits for intravenous infusions. Many of the side effects of CDK4/6 inhibitors and hormonal therapy can be reduced or mitigated with dose adjustments and supportive care contributing to a better quality of life for patients undergoing this treatment [16]. Our findings concur with a recently published case series, which similarly demonstrates efficacy of this well-tolerated combination treatment in a subset of patients impacted by granulosa cell tumors [16].

The addition of CDK4/6 inhibitors to established hormonal therapy treatments is a promising clinical approach in hormone receptor positive cancers. This treatment combination has markedly improved patient outcomes in hormone receptor positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer [8]. Treatment with ribociclib plus letrozole showed improved overall survival compared to placebo in patients with HR-positive, HER2-negative breast cancer [17]. There are now three CDK4/6 inhibitors approved by the United States FDA: palbociclib, ribociclib and abemaciclib. CDK4/6 inhibitors work by downregulating the activity of the cyclin D-CDK4/6 complex. The CDK4/6 complex phosphorylates the Rb protein, which leads to E2F release. This in turn promotes cellular proliferation by enabling continuation to the S phase of the cell cycle [18]. Activation of the CDK4/6 pathway is augmented through hormone receptor signaling and/or by loss of CDKN2A function, which serves as a CDK4/6 inhibitor [19]. Heightened estrogen production in granulosa cells [12] with the loss of CDKN2A in a subset of these tumors [11], provides the premise for combining CDK4/6 inhibitors with hormonal therapy as a strategy to block continuous proliferation of these hormonally regulated neoplasms. The exact biomarkers of response to this combination therapy remain unknown, but can be deduced from insights into mechanisms of resistance to these therapies. Potential mechanisms of resistance to this combination therapy include abnormal activation of cyclin D-CDK4/6, such as CDK6 overexpression, loss or mutation of the Rb protein, and activation of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway, among others [20]. These mechanisms of resistance may play a role in identifying biomarkers and developing new targeted therapies to overcome resistance, which may result in higher treatment efficacy and better tolerability to the patient.

5. Conclusion

Our findings in this case series demonstrate an obvious and durable clinical benefit of concurrent administration of CDK4/6 inhibitors and estrogen blockade in three out of four patients with recurrent GCTs exposed to multiple prior lines of therapy. Importantly, one patient continued to derive benefit with an ongoing complete response that spanned 45 months. We found that this combination therapy was very well tolerated mitigating any discontinuation of treatment due to adverse events. A significant limitation of this study is the small cohort of patients included and the retrospective design which may lead to selection bias and limited generalizability. Although a small sample size, a strength of this study is that the patient cohort reflects the typical treatment course a patient with this rare tumor would experience, having received multiple surgeries and multiple prior treatment regimens. Our case series provides detailed clinical background and supporting evidence for the use of CDK4/6 inhibitors with estrogen blockade as a potential therapy for patients suffereing from recurrent GCTs, particularly those who have been exposed to multiple prior lines of therapy. Though preliminary, the noted durable response suggests that this therapeutic approach may be beneficial for these patients. The efficacy of this combination in recurrent ovarian granulosa cell tumors is promising and warrants further exploration through identification of biomarkers that may be predictive of treatment response and disease progression. Additionally, given the rarity of these tumors, larger, multi-institutional studies are needed to validate treatment outcomes and establish standardized treatment strategies. Prosepective clinical trials through a large cooperative group evaluating the combination of CDK4/6 inhibitors with estrogen blockade in patients with recurrent GCTs are imperative to optimize treatment options for this rare malignancy.

Abbreviations

GCT, granulosa cell tumor; HR, hormone receptor; FDA, Food & Drug Administration; ER, estrogen receptor; PR, progesterone receptor; PFS, progression free survival; CDK, cyclin dependent kinase; FOXL2, forkhead box L2; CDKN2A, cyclin-dependant kinase inhibitor 2A; Rb, retinoblastoma; ERE, estrogen response element; E2F, early region 2 binding factor; IRB, institutional review board; UCLA, University of California, Los Angeles; RECIST, Response evaluation criteria in solid tumors; NED, no evidence of disease; IHC, immunohistochemical; TERT, telomerase reverse transcriptase; AR, androgen receptor; AI, aromatase inhibitor; ABL1, abelson murine leukemia viral oncogene homolog 1; LZTR1, leucine zipper-like transcription regulator 1; SPTA1, spectrin alpha, erythrocytic 1; PIK3CA, phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha; CDKN, cyclin-dependent kinase inhibitor; PET/CT, positron emission tomography/computed tomography; MRI, magnetic resonance imaging; HER2, human epidermal growth factor receptor 2; PI3K, phosphatidylinositol 3-kinase; AKT, protein kinase B; mTOR, mammalian target of rapamycin.

Availability of data and materials

All available data are presented and contained within this article.

Author contributions

AIN, EM, GEK, PV and SM—Conceptualization. GAD, AIN, EM, LR and SM—Data curation. GAD, AIN, EM, LR, SSR and SM—Investigation. GAD, AIN, SSR and SM—Formal Analysis. GEK, OO, PV and SM—Patient data contribution. SSR—Imaging review. GAD and AIN—Visualization. AIN, GAD and SM—Writing-original draft. GAD, AIN, EM, SSR, GEK, LR and SM—Writing-review and editing. All authors have read and agreed to the published version of the manuscript.

Ethics approval and consent to participate

The study was performed with Institutional Review Board (IRB) approval from the University of California, Los Angeles (UCLA: IRB-22-0409 approved on 18 March 2022) and in accordance with the Declaration of Helskinki. The reviewing IRB issued a Waiver of Informed Consent under appropriate regulations for the retrospective review of study data.

Acknowledgment

The authors would like to acknowledge the use of Biorender.com for the availability of high-quality scientific graphics and vector images used to generate figures in this manuscript.

Funding

The authors declare that they did not receive any funding for this study.

Conflict of interest

The authors of this paper declare no conflict of interest of relationships with commercial or financial entities that may influence findings of this manuscript.