Prevalence, clinical characteristics, and outcome of pleural effusions in ovarian cancer

Introduction

Ovarian cancer (OC) encompasses a heterogeneous group of malignancies, over 90% of which are of epithelial origin [1]. Fewer than half of patients with OC survive beyond five years after diagnosis, partly because more than 70% are discovered in an advanced disease stage [1]. OC was the sixth leading cause of 840 tapped malignant pleural effusions (MPEs), after lung, breast, unknown primary, hematological, and gastrointestinal tumors [2]. However, it ranks third if only women are being considered [3]. OC often initially manifests with a pleural effusion (PE). In a retrospective analysis of 32 consecutive OC women with MPE, the effusion was among the presenting symptoms of cancer in 24 (75%) cases [4].

Few studies have addressed the prognostic significance of PEs in the context of specific primary malignancies. For example, PEs, including those too small to be aspirated, have been found to be an independent predictor of poor survival in lung cancer [5] and diffuse large B-cell lymphoma [6]. The only two such studies conducted in OC provided a partial view of the problem because they included a very select population. One analyzed a small number of patients with cytology-proven MPEs who underwent optimal abdominopelvic cytoreductive surgery [7], while the other focused on PEs detected before a primary debulking surgery for advanced cancer grades [8]. In the current investigation we aimed, for the first time, to systematically analyze the etiology, clinical characteristics, and outcomes of PEs at any OC stage, as well as the influence they may have on overall survival (OS) and progression-free survival (PFS).

Materials and methods

Results

Survival

At the end of the study, 112 (59%) patients had died and the median follow-up time for the remaining 77 was 59.1 (25.8–80.1) months. Median OS for the entire cohort was 48.5 months (95%CI 33.8–63.2). Women with PEs survived less than those without PEs (26.7 months, 95%CI 22–31.3 vs. 90.4 months, 95%CI 46.2–134.6; p<0.001). Specifically, OS was significantly lower in the subgroup of patients with either MPEs (24.2 months, 95%CI 17.5–30.9) or PEs of uncertain origin (27.4 months, 95%CI 18.3–36.5) as compared to the non-PE group (p<0.001) (Figure 1). Although there was a trend toward a better OS in women whose PEs appeared during the disease course (34.5 months, 95%CI 25.4–43.5) in contrast to those with PEs at the time of OC diagnosis (20.8 months, 95%CI 13.9–27.7), it did not reach statistical significance (p=0.296).

Figure 1:

Median overall survival of ovarian cancer patients according to the pleural effusion status.

OS, overall survival; MPE, malignant pleural effusion; PE, pleural effusion.

A multivariate analysis using the Cox regression model was performed, after entering the following variables as potential prognostic factors: age, serum CA 125 ≥ 1,200 U/mL at diagnosis, FIGO stage, ECOG, OC histological type, metastatic pattern, presence of PEs, volume of PEs >250 mL, pleural nodularity and/or thickening on CT scans, ascites, as well as surgical therapy and its results (optimal or suboptimal cytoreduction). As shown in Table 2, the presence of PE was one of the strongest predictors of decreased survival (hazard ratio [HR] 9.73). Exclusion of the six postsurgical PEs for the calculations did not change results (data not shown).

Table 2:

Cox proportional hazard models assessing overall survival of OC patients.

Variable	Adjusted HR (95%CI)	p-Value
Presence of PE	9.73 (4.19–22.6)	<0.001
No surgical treatment	7.46 (4.19–13.30)	<0.001
Peritoneal metastases	4.77 (1.49–15.27)	0.009
PE volume >250 mL	2.12 (1.31–3.43)	0.002
Suboptimal cytoreductive surgery	1.97 (1.20–3.24)	<0.001

1. CI, confidence interval; HR, hazard ratio; OC, ovarian cancer; PE, pleural effusion.

Median PFS of the study population was 21.9 months (95%CI 18.3–25.6). It was lower in the PE cohort (9.8 months, 95%CI 8.4–11.6) than in the non-PE group (55.3 months, 95%CI 15.6–95; p<0.001) (Figure 2). MPEs and PEs of uncertain etiology exhibited similar PFS (10 months, 95%CI 8.7–11.3 vs. 8.1, 95%CI 5.7–10.5; p=0.593) (Figure 2). There was also a nonsignificant tendency toward a better PFS when PEs developed during follow-up rather than being discovered at the time of OC diagnosis (12.6 months, 95%CI 8–17.2 vs. 8.1 months, 95%CI 5.5–10.6; p=0.081).

Figure 2:

Median progression-free survival of ovarian cancer patients stratified for pleural effusion status.

MPE, malignant pleural effusion; PE, pleural effusion; PFS, progression-free survival.

The multivariate Cox regression model showed that, for the same variables as those previously mentioned for the OS statistical model, PEs were included among the most significant predictors of a poor PFS (HR 3.87) (Table 3).

Table 3:

Cox proportional hazard models assessing progression-free survival of OC patients.

Variable	Adjusted HR (95%CI)	p-Value
Lung metastases	6.27 (3.17–12.4)	<0.001
No surgical treatment	5.10 (2.71–9.60)	<0.001
Presence of PE	3.87 (2.52–5.96)	<0.001
Suboptimal cytoreductive surgery	2.81 (1.79–4.41)	<0.001

1. CI, confidence interval; HR, hazard ratio; OC, ovarian cancer; PE, pleural effusion.

Discussion

To our knowledge, this study represents the first simultaneous evaluation of the prevalence, clinical and PF features, and prognosis of PEs in women with OC. PEs occurred in 43% of the cases, using CT as the reference standard, and independently contributed to mortality and PFS.

Most OC were diagnosed at FIGO stages III (51%) and IV (30%). Since PE with positive cytology defines FIGO stage IVA, reasonably the majority of detected PEs fell into the advanced stages III (39.5%) and IV (53%). The overall prevalence of PEs in OC (43%) was quite similar to that reported for other primary tumors that metastasize to the pleura, such as lung cancer (40%) [5] or diffuse large B-cell lymphoma (30%) [6]. Pleural nodularity or thickening characterized 27% of MPEs in OC women, which is somewhat lower than the 43% general prevalence of these specific radiological signs in pleural malignancies [11]. However, the potential malignant nature of PEs that were classified as being of uncertain origin cannot be excluded (16.7% of which exhibited pleural nodules and/or thickening). Also, in the context of an OC, it was found that the larger the accompanying PE, the more likelihood of being malignant. This is not surprising, considering that malignancy accounts for more than half of large or massive PEs [12]. In a study of 16 OC patients with MPEs and 22 with nonmalignant PEs, moderate to large amounts of PF (81.3 vs. 9.1%) and pleural nodules (50 vs. 0%), along with supradiaphragmatic lymph node enlargement (75 vs. 9.1%) predominated in the former group and, therefore, these CT signs increased the probability for a PE to be malignant [13].

The yield of PF cytological examinations seems to be particularly high in MPEs secondary to OC as compared to other tumor types. While the overall sensitivity of PE cytology for identifying malignancy is around 55% [14], it was found this percentage reached 79% in our cohort of OC women, which is in line with other reports. For example, in four series comprising 27, 31, 38, and 96 MPEs due to OC, the respective PF cytological yields were 83, 84, 94.7, and 78% [15], [16], [17], [18], though no information on the number of fluid specimens processed and the way they were examined (whether smears and/or cell blocks) were provided. Another point was that MPEs in OC were symptomatic enough to require definitive pleural procedures, either bedside pleurodesis or insertion of an indwelling pleural catheter, in 60% of the cases. This percentage compares with that observed in a multicenter cohort of 537 MPEs from a variety of tumor types (OC representing only 5.8% of the cases), where 288 (53.6%) eventually needed to be treated with pleurodesis and/or indwelling pleural catheters [19].

The mechanism of metastatic pleural involvement in OC is speculative and probably includes one or more of the following: a) invasion from an affected contiguous diaphragm, b) migration of tumor cells from the peritoneal cavity to the pleural space through small diaphragmatic defects, and c) hematogenous spread. The relevance of the first two potential ways of cancer dissemination was supported by the finding of ascites and peritoneal metastases (which encompasses peritoneal diaphragmatic implants) as independent predictors of PE development.

Our survival analysis showed that women with PEs (particularly PEs of at least 250 mL), had worse OS and PFS than those without PEs after adjustment for confounders. A pair of prior studies cast a sobering light on the prognostic impact of PEs in OC women. In an earlier retrospective study, 21 OC patients with stage IVA (due to MPEs), who underwent tumor debulking to less than 1 cm of residual disease followed by platinum-based chemotherapy, had a shorter time to recurrence (12 vs. 21 months, p=0.04) and decreased OS (30 vs. 58 months, p=0.016) compared to 76 similarly treated patients with stage IIIC [7]. However, CT scans were not used for staging and, therefore, the existence of undetected intrathoracic disease could not be excluded. In a second study from the same institution, the preoperative CT images of 172 stage III and 31 stage IV OC women undergoing primary cytoreduction were retrospectively evaluated [8]. The prevalence of PEs at diagnosis (62 patients, 30.5%) was almost identical to that observed in our study. However, only 19 (30%) were tapped, of which 16 were deemed to be malignant. In both stages III and IV the presence of PEs occupying one-third or more of the hemithorax was independently associated with worse OS in a multivariate analysis (HR=2.27) [8].

A novel finding of our study is that even trace effusions not amenable to tapping confer a survival disadvantage, with a differential life expectancy of 63 months as compared to patients without PEs. It can be hypothesized that many of these minimal effusions are actually MPEs which go unnoticed due to the difficulty of performing conventional diagnostic procedures. It should be stressed that an accurate identification of the presence and extent of pleural involvement, though paramount for determining prognosis and selecting appropriate treatment, is difficult by noninvasive means. The true pleural status revealed during video-assisted thoracoscopic surgery (VATS) do not always correlate with the CT features considered suggestive of pleural malignancy (i.e., thickening and/or nodularity) [20], nor with the PF cytology results [18], [19], [20], [21]. For instance, in a series of 44 advanced OC patients who underwent VATS, 10 and 16 had pleural nodules and pleural thickening suspicious of malignancy on preoperative CT scans, respectively [20]. However, thoracoscopic biopsies did not confirm pleural tumor invasion in two and six of these cases. In a recent study, VATS was performed on 100 women with advanced OC and PEs occupying one-third or more of the pleural cavity [18]. Macroscopic pleural disease was identified in 70% and was independently associated with elevated death risk. Interestingly, 29% of patients with negative PF cytology had gross macroscopic disease at VATS [18]. Conversely, no gross pleural disease is seen during VATS procedures in around 25% of OC patients with positive PF cytology [21]. These data support the indication of VATS in all OC women with moderate to large PEs in order to confirm macroscopic pleural disease that may impact management [18]. Currently, it has not been established whether bulky pleural involvement is present in OC women with small PEs and if VATS could be beneficial in these patients.

Our study has several limitations. First, our cohort was sourced from a single institution and spanned a relatively long-period of time during which therapeutic approaches have varied. Second, the sample size was moderate and the study design retrospective, though there were very little missing data. Third, our reference standard for some MPEs (those labeled as probable MPEs) was imperfect, but widely accepted in medical literature. Finally, 44% of PEs could not be analyzed due to their small volume which, on the other hand, reflects daily clinical practice. Yet demonstration of the poor outcome of these minimal PEs is a relevant fact.

In summary, PEs are frequently encountered in OC women and portend a poor prognosis, even those of such a small size that a diagnostic thoracentesis cannot be performed safely. Nearly two-thirds of MPEs associated with OC need definitive pleural procedures, either pleurodesis or indwelling pleural catheters, for symptomatic control. Whether minimal PEs harbor undiagnosed pleural involvement should be explored in future investigations.