October 2005
Volume 46, Issue 10
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Anatomy and Pathology/Oncology  |   October 2005
Histopathological Features and P-glycoprotein Expression in Retinoblastoma
Author Affiliations
  • João Pessoa Souza Filho
    From the Department of Ophthalmology, Federal University of São Paulo, São Paulo, Brazil; and the
    Henry C. Witelson Ocular Pathology Laboratory, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada.
  • Zelia Maria S. Correa
    Henry C. Witelson Ocular Pathology Laboratory, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada.
  • Alexandre N. Odashiro
    From the Department of Ophthalmology, Federal University of São Paulo, São Paulo, Brazil; and the
    Henry C. Witelson Ocular Pathology Laboratory, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada.
  • Anamaria Baptista Coutinho
    From the Department of Ophthalmology, Federal University of São Paulo, São Paulo, Brazil; and the
    Henry C. Witelson Ocular Pathology Laboratory, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada.
  • Maria Cristina Martins
    From the Department of Ophthalmology, Federal University of São Paulo, São Paulo, Brazil; and the
  • Clélia Maria Erwenne
    From the Department of Ophthalmology, Federal University of São Paulo, São Paulo, Brazil; and the
  • Miguel N. Burnier, Jr
    Henry C. Witelson Ocular Pathology Laboratory, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada.
Investigative Ophthalmology & Visual Science October 2005, Vol.46, 3478-3483. doi:10.1167/iovs.04-1290
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      João Pessoa Souza Filho, Zelia Maria S. Correa, Alexandre N. Odashiro, Anamaria Baptista Coutinho, Maria Cristina Martins, Clélia Maria Erwenne, Miguel N. Burnier; Histopathological Features and P-glycoprotein Expression in Retinoblastoma. Invest. Ophthalmol. Vis. Sci. 2005;46(10):3478-3483. doi: 10.1167/iovs.04-1290.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

purpose. To investigate the expression of P-glycoprotein (P-gp) in retinoblastoma specimens enucleated as a primary treatment or after conservative treatment and to correlate this expression with histopathological tumor features.

methods. Retrospective analysis was performed on retinoblastoma specimens obtained consecutively between 1993 and 2003 by enucleation either as primary treatment (group I) or after the failure of conservative treatment (group II). Sections from the formalin-fixed, paraffin-embedded specimens were stained with hematoxylin and eosin. Group I tumor differentiation was classified according to the percentage of Flexner-Wintersteiner rosettes. Group II tumors, categorized as viable-appearing, regressed with a well-differentiated component (WDC), and regressed. Other features, such as choroidal and optic nerve invasion, were evaluated. P-gp expression was graded semiquantitatively as negative, low, or high. Variables were statistically analyzed by χ2 and Student’s t-tests.

results. Histopathological assessment of group I revealed 65% moderately differentiated tumors, 30% well differentiated, and 5% poorly differentiated. Fifteen percent had optic nerve tumor invasion only, 20% choroidal invasion only, and 55% both choroidal and optic nerve invasion. Group II had 62.5% well-differentiated, regressed tumors; 25% had regressed tumors replaced by glial scarring; and 12.5% had tumors containing viable, poorly differentiated cells. Approximately 18% had choroidal tumor invasion only, 6.3% optic nerve tumor invasion only, and 6.3% simultaneous optic nerve and choroidal invasion. P-gp expression was observed in 60% of group I and 66.6% of group II. All P-gp-positive cases in group II had a high expression. P-gp was also expressed by 81.2% of well-differentiated tumors.

conclusions. P-gp was expressed more frequently by well-differentiated retinoblastomas, especially those treated by chemotherapy before enucleation. This finding could be related to treatment failure.

Retinoblastoma (Rb) is currently considered to be a highly curable malignant tumor, with an overall 3-year survival rate of more than 90%. 1 2 Before the 1990s, the standard approach to unilateral Rb was enucleation. Bilateral cases were usually treated by enucleation of the worst eye and external beam radiation therapy (EBRT) in the other eye. Chemotherapy was reserved during this period for high-risk and metastatic Rb. 1  
In an attempt to preserve vision and avoid enucleation and the complications associated with EBRT, new drug regimens were developed, and chemotherapy is currently considered to be an important modality for the treatment of Rb. 1 3 Chemotherapeutic drugs induce tumor regression and therefore allow for focal treatments such as photocoagulation, 4 thermotherapy, 5 and cryotherapy. 6 However, intraocular or local Rb recurrence continues to be a major problem, even with the use of multidrug regimens. 7 Local tumor recurrence in such cases could suggest a lack of response to chemotherapy also known as tumor resistance. 8  
A recent publication described the histopathological features of Rb treated with chemotherapy and observed that several tumors showed residual areas of well-differentiated cells. 3  
Multidrug resistance (MDR) of various human tumors has been linked to elevated expression of particular proteins, such as cell membrane transporters, which can cause an increased efflux of cytotoxic drugs from the cancer cells. 9 10 11 12 Although there are other known proteins linked to chemoresistance, which include MRP, LRP, BCRP, and CMOAT, one of the best-described mechanisms is P-glycoprotein (P-gp). 11 13 P-gp is a 170-kDa plasma membrane protein reported to have a role in chemotherapy outcome in humans. 9 10 14 15 16 In tumors such as neuroblastoma and sarcoma, the presence of P-gp before treatment has shown a strong association with poor treatment outcome. 9 16 17  
Unfortunately, a similar correlation is almost impossible to establish in Rb, because of the high risk of neoplastic dissemination associated with intraocular surgery and biopsy of these tumors. However, in a few extraocular Rb cases, it has been possible to collect tissue samples that later revealed a correlation between P-gp expression and local treatment failure. 18 Another publication showed P-gp expression in 25% of Rb enucleated before chemotherapy and in 100% of the tumors that had been treated with chemotherapy, suggesting that this expression could be related to the local treatment failure observed in these tumors. 19 The few studies investigating P-gp expression in Rb have been focused on the relationship between the expression of this protein and chemotherapy failure in the primary tumor. 18 19 20 21  
The purpose of this study was to investigate P-gp expression in Rb specimens obtained by primary or secondary enucleation and to correlate this expression with histopathological tumor features. 
Methods
The specimens of patients with Rb treated by enucleation between 1993 and 2003, either as a form of primary treatment or because of conservative treatment failure, were included in the study. Patient information and formalin-fixed, paraffin-embedded specimens were obtained from the Pathology Registry of the Federal University of São Paulo (UNIFESP), Brazil. The Institution’s Review and Ethics Committee approved the study. New sections of these blocks were stained with hematoxylin and eosin (H&E) to be reviewed by two ophthalmic pathologists at the Henry C. Witelson Ocular Pathology Laboratory and Registry, Montreal, Canada. The tissue and medical records were obtained and managed in accordance with guidelines of the Declaration of Helsinki. 
Tumor differentiation in group I was classified according to the estimated percentage of Flexner-Wintersteiner rosettes in the available sections. Tumors considered well differentiated had to present rosettes in >80% of their areas. Poorly differentiated tumors did not present rosettes, and the remaining cases were classified as moderate. 22  
Previously treated tumors were included in group II and classified as viable-appearing Rb, regressed Rb with a well-differentiated component (WDC), and regressed Rb. A viable-appearing Rb was composed of poorly differentiated cells, whereas a regressed Rb with WDC was composed of cells with the presence of Flexner-Wintersteiner rosettes, retinoma, and/or retinocytoma-like features and a regressed Rb, composed of glial scarring that replaced the tumor. 3  
Other histopathologic features, such as choroidal and optic nerve invasion were evaluated in both groups, as described by Khelfaoui et al. 23 The degree of choroidal invasion was classified in five subgroups: I, no invasion; II, minimal invasion (tumor cells destroying Bruch’s membrane without invading the choroid to any depth); III, massive invasion (any choroidal involvement that is not minimal); IV, intrascleral invasion; and V, extrascleral invasion. Optic nerve tumor invasion was classified in four subgroups: I, no invasion; II, prelaminar invasion; III, postlaminar invasion; and IV, invasion through the resection line and/or subarachnoid space. 
The immunohistochemical P-gp expression assay consisted of several steps. Four-micrometer-thick specimen sections were deparaffinized with xylene and rehydrated through graded ethanol washes. Endogenous peroxidase activity was blocked by a 10-minute wash of 3% hydrogen peroxide-methanol. To optimize P-gp immunostaining, antigen exposure was performed by microwave heating of the sections in citrate buffer (pH 6.0) for 15 minutes. Nonspecific protein binding was blocked using a 1% bovine serum albumin (BSA)/Tris-buffered saline (TBS, pH 7.6) solution during a 30-minute wash. Sections were incubated with a monoclonal mouse anti-P-gp antibody (clone C494; NeoMarkers, Fremont, CA) and diluted 1:50. After a 30-minute incubation with the primary antibody at room temperature, sections were washed and incubated with biotinylated rabbit anti-mouse secondary antibody (Dako, Mississauga, Ontario, Canada) and diluted 1:500 for 30 minutes at 37°C. Sections were then incubated with horseradish peroxidase–conjugated streptavidin-biotin complex (Dako) for 30 minutes at 37°C. Immunostaining visualization was enabled by the 3-amino-9-ethylcarbazole (AEC) chromogen (Dako). Sections were lightly counterstained with hematoxylin and coverslipped. Negative controls were obtained either by omitting the primary antibody or by using a nonimmune serum (0.1% BSA/TBS). Positive control experiments were performed on adrenal gland sections. 
Two ophthalmic pathologists independently analyzed the immunostained sections by light microscopy, and the final interpretation was based on agreeing assessments. P-gp expression was graded semiquantitatively as negative (−), no cells stained; low (+), up to 50% of viable tumor cells stained positive; or high (++), more than 50% of viable tumor cells stained positive. 
Patient data collected included age at the time of surgery (in months), gender, race, laterality, and conservative treatment used, such as chemotherapeutic drug regimens. 
Statistical analysis used both χ2 and Student’s t-tests, both of which produce odds ratios and corresponding 95% confidence intervals. Statistical significance was set at P < 0.05. Intra- and interobserver agreements for P-gp immunostain classifications were measured by the κ coefficient. Statistical-analysis software (Statistical Package for the Social Sciences ver. 11.5; SPSS Inc., Chicago, IL) was used for all statistical tests. 
Results
The ocular specimens of 36 patients were divided into two groups: group I, 20 eyes managed by enucleation as a primary treatment, and group II, 16 eyes enucleated after previous treatments. Group I was composed of 60% boys (n = 12) and 40% girls (n = 8). The tumor was unilateral in 75% of the cases (n = 15) and bilateral in 25% (n = 5). The mean age of patients was 31 ± 22.3 months at the time of surgery. Group II (n =16) was composed of 56.2% boys (n = 9) and 43.8% girls (n = 7). The tumor was unilateral in 31.3% of the cases (n = 5) and bilateral in 68.7% (n = 11). The mean age of this group of patients was 19.6 ± 15.1 months. Nine (56.2%) of the patients in group II were treated by chemotherapy alone; three (18.8%) by chemotherapy and laser, three (18.8%) by chemotherapy and EBRT, and one (6.2%) by chemotherapy, laser, and iodine-125 plaque radiotherapy (I-125). 
Although both groups had advanced disease, there was no significant difference between the groups in variables such as age (P = 0.09), sex (P = 0.82), and the eye (right or left) involved (P = 0.82). However, a significant difference in tumor laterality (uni- or bilateral) was observed between the two groups (P = 0.009). 
Histopathological assessment of group I revealed 13 (65%) moderately differentiated tumors, 6 (30%) well differentiated, and 1 (5%) poorly differentiated. Three (15%) eyes had optic nerve tumor invasion only, 4 (20%) had choroidal tumor invasion only, and 11 (55%) had simultaneous choroidal and ON invasion (Table 1)
Histopathologic assessment of group II revealed 10 (62.5%) eyes containing a regressed Rb with a WDC, 4 (25%) eyes containing regressed Rb with glial scarring replacing the tumor and 2 (12.5%) containing viable-appearing Rb with poorly differentiated tumor cells. Three (18.7%) eyes had choroidal tumor invasion only, one (6.3%) eye had optic nerve tumor invasion only, and one (6.3%) had simultaneous optic nerve and choroidal invasion (Table 2) . There was a statistically significant difference between the two groups in regard to variables such as degree of ocular layer tumor invasion and optic nerve tumor invasion (P = 0.03 and P = 0.01, respectively). 
Considering all the specimens included in this study (n = 36), 20 Rbs containing apparently viable cells were P-gp positive: 12 in group I (n = 20) and 8 in group II (n = 16). There was no significant difference in P-gp expression between the two groups (P = 0.706). However, when considering the differences in degree of expression between the two groups, 50% of eyes that were P-gp positive in group II (4/8) showed a high expression of the protein (++; Figs. 1 2 ). Meanwhile, none of the eyes in group I expressed P-gp to the same extent (0/12; P = 0.006; Tables 1 2 ). 
The patients whose eyes expressed P-gp had an average age of 27 ± 18.1 months, whereas the ones with eyes that did not express P-gp were an average of 25.2 ± 24.9 months old at the time of surgery. The difference between the two groups was not statistically significant. 
Considering all the patients, P-gp expression was observed in 81.2% (13/16) of the well-differentiated tumors and in 53.8% (7/13) of the moderately differentiated tumors. When the degree of P-gp expression in well-differentiated tumors versus moderately or poorly differentiated tumors is compared, it is notable that the more differentiated tumors expressed the protein more intensely and the difference was statistically significant (P = 0.028). 
Considering tumor laterality, 15 of the 19 unilateral tumors expressed P-gp, whereas 5 of 13 bilateral tumors were P-gp positive. This difference was again statistically significant (P = 0.02). 
Intraobserver agreement regarding the immunohistological slides was 91.2% (κ coefficient = 0.82), and the interobserver agreement was 80.5% (κ coefficient = 0.70). 
Discussion
Various investigators have assessed Rb invasiveness, recurrence, and metastatic potential. 3 As a result, publications have adopted slightly different histopathological classifications of primary enucleated eyes, as opposed to previously treated eyes. 3 The main difference seems to be the inclusion of specific parameters for the previously treated eyes, such as cell viability and the presence of fibrovascular scar tissue. The use of different classification systems, although initially confusing for some, serves the purpose of comparing our findings to other publications. 3  
Regarding local tumor invasiveness, this study revealed a higher degree of ocular layers and optic nerve tumor invasion in group I, and there was a statistically significant difference between the two groups. In the evaluation of neoplastic histologic features, it would be expected that untreated tumors would be more aggressive than previously treated ones. Another significant finding was the predominant P-gp expression among unilateral tumors that did not correlate with previous treatment or cell differentiation. This isolated finding could be due to chance alone. 
The presence of tumor beyond the lamina cribrosa is a risk factor for metastatic disease, 24 25 and although the choroidal invasion has been considered an important risk factor for metastatic disease because it allows for access to sclera and emissary vessels, it is not clear whether choroidal invasion alone necessitates the use of systemic chemotherapy. 24  
Chemotherapeutic drugs are known to have a variable response and do not achieve complete neoplastic regression in many instances, probably as a result of different sensitivity of the Rb cell to the same treatment. 26 Some reports have shown new tumor development even after multidrug chemotherapeutic regimens. 7 It is also known that local tumor relapses and therapeutic failures are the most common causes of death in children with cancer. 13 None of the patients included in this study had clinical chart annotations of new tumor foci, but two had recurrent or residual tumor growth in the same site of the initial treated lesion. It is interesting to observe that most unilateral Rbs were P-gp positive in our series, and these tumors tended to be unifocal. There is a reported correlation between P-gp expression and MDR in cancer. 9 10 11 12 A variety of other molecular markers have also been shown to be associated with MDR, although the roles they play are not complete understood. 27 MDR in human tumors estimated by P-gp gene expression ranges from 11% to 100%, depending on the method used. 9  
P-gp functions as an adenosine triphosphate–dependent drug efflux pump of broad specificity, and it causes drug resistance by reducing the net intracellular accumulation of cytotoxic drugs. There are two genes related to classic MDR in humans MDR1 and MDR2/MDR3. Of these, only MDR1 has been shown to cause MDR in gene transfection studies. 9 13 14 15  
Several publications have considered P-gp tumor expression to be an advanced prognostic factor, regardless of the disease period in which it is assessed. Also, increased levels of P-gp expression are associated with an unfavorable prognosis in neuroblastomas and sarcomas. 9 15 16 18 These publications prompted the study of P-gp expression, leading to this article. 
An in vitro study showed that approximately 30% of cell lines from Rbs that had been enucleated as a primary treatment and 100% of cell lines originating from Rb tumors that had been treated by chemotherapy were resistant to multiple chemotherapeutic agents routinely used to treat this tumor. 28 A subsequent study revealed that tumor cells with the MDR phenotype expressed P-gp, as opposed to cells with multidrug sensibility that were P-gp negative. 14 These findings raise a controversy as to whether P-gp-positive tumors do not respond to chemotherapy because of cell differentiation or whether chemotherapy is efficient in destroying all undifferentiated areas of such tumors, leaving subpopulations of well-differentiated, resistant cells that are likely to be responsible for a future recurrence. 19 Still, P-gp is more frequently expressed in Rbs that do not respond to chemotherapy than ones not previously treated. This finding suggests, once again, a correlation between P-gp expression and the failure of treatment. 18 Similarly, the results obtained in this study revealed a more intense P-gp expression in tumors previously treated by chemotherapy. 
A study has been published demonstrating that Rb cellular differentiation may affect tumor response and that highly differentiated components of Rb are comparatively more resistant to irradiation than are other areas of the tumor. 29 In this series, there was a clear, well-differentiated component in most tumors expressing P-gp. This finding suggests the likelihood that well-differentiated tumor cells show similar resistance to chemotherapy, as described for radiotherapy, prompting speculation about the role of chemotherapy in inducing Rb differentiation 3 or perhaps the resistant cells being those that are more differentiated, not actively dividing when exposed to chemotherapy, therefore surviving to grow later and causing the treatment to fail. 
Finally, P-gp expression has been observed twice as frequently in Rbs that were previously treated by chemotherapy. Interesting enough, previously treated tumors that did not express P-gp had received cyclosporine, 18 which was not used in any of the cases included in the present series. 
A current concern is how MDR can be prevented. This problem has been addressed by adding cyclosporine to a regimen of vincristine, etoposide, and carboplatin. The concurrent administration of cyclosporine seems to abrogate the efflux of drug from the cancer cell. 20 21 Although the successful treatment of Rb using cyclosporine has been published, 20 21 the high dosage necessary to affect P-gp expression can also be very toxic and debilitating for the patient. 11 30 31 Also important is an ongoing phase II study, “Neoadjuvant High-Dose Carboplatin and Etoposide, Vincristine, and Cyclosporine Followed by Ophthalmic Focal Therapy Comprising Cryotherapy and/or Laser Therapy in Patients with Newly Diagnosed Unilateral or Bilateral Intraocular Retinoblastoma,” funded by the National Cancer Institute. This study seeks to examine the efficacy of the regimen including cyclosporine, compared with the published data without cyclosporine, in terms of increasing the proportion of eyes that remain relapse free and do not require external beam radiotherapy and/or enucleation, as well as determining the toxicity of the regimen in these patients. Currently, recently developed specific inhibitors of P-gp, like laniquidar and diarylimidazole, are undergoing study as more effective, specific, and less toxic drugs than cyclosporine. 11 Future studies are needed to determine more effective and less toxic drugs that have minimal or no effect on P-gp expression. 
In the face of these facts, the correlation between P-gp expression and MDR perhaps should be considered before changing the management of an uncontrolled intraocular Rb, nonresponsive to chemotherapy in the only remaining eye of a child. 14  
In conclusion, this study showed that P- gp was expressed more frequently by well-differentiated Rbs, especially tumors treated by chemotherapy before enucleation. This finding could lead to various hypotheses to explain the failure of treatment. 
 
Table 1.
 
Histopathology Findings and P-gp Expression in Group I
Table 1.
 
Histopathology Findings and P-gp Expression in Group I
Rb Differentiation P-gp Expression Degree of Invasion*
Choroid ON
1 MD + I I
2 MD + III III
3 WD III III
4 WD + III I
5 MD III III
6 MD + II III
7 MD III III
8 WD + II I
9 PD I III
10 WD + II II
11 MD + III III
12 MD + III I
13 WD + II II
14 MD + III IV
15 MD + I III
16 WD + I II
17 MD III IV
18 MD I I
19 MD III II
20 MD III I
Table 2.
 
Histopathology Findings and P-gp Expression in Group II
Table 2.
 
Histopathology Findings and P-gp Expression in Group II
Rb Viable Cells* Differentiation Classification P-gp Expression, † Degree of Invasion, ‡
Choroid ON
1 + Well Regressed with WDC + I II
2 + Well Regressed with WDC ++ I I
3 + Well Regressed with WDC I I
4 + Well Regressed with WDC + III I
5 + Well Regressed with WDC I I
6 Regressed I I
7 + Well Regressed with WDC + III I
8 Regressed I I
9 + Poor Viable RB III II
10 + Well Regressed with WDC ++ I I
11 + Poor Viable RB I I
12 + Well Regressed with WDC ++ III I
13 + Well Regressed with WDC ++ I I
14 Regressed I I
15 Regressed I I
16 + Well Regressed with WDC + I I
Figure 1.
 
(A) Photomicrograph of an H&E-stained microslide of an Rb specimen treated by chemotherapy before enucleation, revealing a well-differentiated tumor composed of rosettes (arrows). (B) Photomicrograph of a P-gp positive specimen. Note the well degree of cell differentiation. Arrows: P-gp-positive rosettes. Magnification: (A) ×200; (B) ×320.
Figure 1.
 
(A) Photomicrograph of an H&E-stained microslide of an Rb specimen treated by chemotherapy before enucleation, revealing a well-differentiated tumor composed of rosettes (arrows). (B) Photomicrograph of a P-gp positive specimen. Note the well degree of cell differentiation. Arrows: P-gp-positive rosettes. Magnification: (A) ×200; (B) ×320.
Figure 2.
 
(A) Photomicrograph of an Rb specimen from an enucleated eye reveals negative P-gp expression in an area of Flexner-Wintersteiner rosettes (arrow). (B) Photomicrograph shows positive P-gp expression in a tumor of similar cell differentiation. Arrow: area of P-gp expression. Magnification: ×640.
Figure 2.
 
(A) Photomicrograph of an Rb specimen from an enucleated eye reveals negative P-gp expression in an area of Flexner-Wintersteiner rosettes (arrow). (B) Photomicrograph shows positive P-gp expression in a tumor of similar cell differentiation. Arrow: area of P-gp expression. Magnification: ×640.
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Figure 1.
 
(A) Photomicrograph of an H&E-stained microslide of an Rb specimen treated by chemotherapy before enucleation, revealing a well-differentiated tumor composed of rosettes (arrows). (B) Photomicrograph of a P-gp positive specimen. Note the well degree of cell differentiation. Arrows: P-gp-positive rosettes. Magnification: (A) ×200; (B) ×320.
Figure 1.
 
(A) Photomicrograph of an H&E-stained microslide of an Rb specimen treated by chemotherapy before enucleation, revealing a well-differentiated tumor composed of rosettes (arrows). (B) Photomicrograph of a P-gp positive specimen. Note the well degree of cell differentiation. Arrows: P-gp-positive rosettes. Magnification: (A) ×200; (B) ×320.
Figure 2.
 
(A) Photomicrograph of an Rb specimen from an enucleated eye reveals negative P-gp expression in an area of Flexner-Wintersteiner rosettes (arrow). (B) Photomicrograph shows positive P-gp expression in a tumor of similar cell differentiation. Arrow: area of P-gp expression. Magnification: ×640.
Figure 2.
 
(A) Photomicrograph of an Rb specimen from an enucleated eye reveals negative P-gp expression in an area of Flexner-Wintersteiner rosettes (arrow). (B) Photomicrograph shows positive P-gp expression in a tumor of similar cell differentiation. Arrow: area of P-gp expression. Magnification: ×640.
Table 1.
 
Histopathology Findings and P-gp Expression in Group I
Table 1.
 
Histopathology Findings and P-gp Expression in Group I
Rb Differentiation P-gp Expression Degree of Invasion*
Choroid ON
1 MD + I I
2 MD + III III
3 WD III III
4 WD + III I
5 MD III III
6 MD + II III
7 MD III III
8 WD + II I
9 PD I III
10 WD + II II
11 MD + III III
12 MD + III I
13 WD + II II
14 MD + III IV
15 MD + I III
16 WD + I II
17 MD III IV
18 MD I I
19 MD III II
20 MD III I
Table 2.
 
Histopathology Findings and P-gp Expression in Group II
Table 2.
 
Histopathology Findings and P-gp Expression in Group II
Rb Viable Cells* Differentiation Classification P-gp Expression, † Degree of Invasion, ‡
Choroid ON
1 + Well Regressed with WDC + I II
2 + Well Regressed with WDC ++ I I
3 + Well Regressed with WDC I I
4 + Well Regressed with WDC + III I
5 + Well Regressed with WDC I I
6 Regressed I I
7 + Well Regressed with WDC + III I
8 Regressed I I
9 + Poor Viable RB III II
10 + Well Regressed with WDC ++ I I
11 + Poor Viable RB I I
12 + Well Regressed with WDC ++ III I
13 + Well Regressed with WDC ++ I I
14 Regressed I I
15 Regressed I I
16 + Well Regressed with WDC + I I
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