Improved flow cytometric determination of proliferative activity (S-phase fraction) from paraffin-embedded tissue

Effects of resolution reduction on data analysis

BACKGROUND

There is often a need in flow cytometry to display and analyze histograms at resolutions lower than those native to the data. It is common, for example, to analyze DNA histograms at 256-channel resolution, even though the data were acquired at 1,024 channels or more. The most common method for reducing resolution, referred to as the consecutive summation (CS) method, can introduce distortions into the shape of histograms. Peaks that were symmetric in the original data can become skewed in the reduced-resolution histogram. Data analysis can be negatively affected by the distortions produced by reducing the histogram resolution. An alternative technique for reducing histogram resolution, the unbiased summation (US) method, minimizes shape distortion. This paper describes the US method and examines the benefits it provides in the analysis of DNA histograms.

METHODS

Reduced chi-square (RCS) was used to measure the response to three experimental variables in the least-squares analysis of simulated DNA histograms. For each variable (the percentage of coefficient of variation [%CV], number of events, and mean position of the G1 distribution), a test data set of 1,000 histograms was generated at 1,024-channel resolution. Histogram resolutions were reduced with each method and then analyzed with ModFit LT cell-cycle analysis software (Verity Software House, Topsham, ME). S-phase error and processor computation time of each method also were evaluated. A Monte Carlo experiment was performed to compare CS and US methods to theoretically correct reductions.

RESULTS

CS method analysis results were negatively affected by changes in %CV, number of events, and G1 peak position. The US method produced consistently lower RCS values (more accurate results) within the tested ranges. The US method eliminated bias in S-phase error and had negligible impact on analysis processing speed. It improved RCS values 44.50% on average (P < 0.0002) with actual DNA histograms. Whereas the CS method became less accurate (chi-square test) as the amount of reduction increased, the US method was unaffected, producing consistently better results.

CONCLUSIONS

The US method is recommended for reducing histogram resolution in modeling applications such as DNA cell-cycle analysis. It may have implications in other areas of flow cytometric data analysis.

Hepatocyte proliferation and risk of hepatocellular carcinoma in cirrhotic patients

OBJECTIVES

High hepatocyte proliferation has been recently proposed as a risk factor for the development of hepatocellular carcinoma (HCC). The aim of this study was to assess whether hepatocyte proliferation is an independent risk factor for HCC when considered together with clinical and demographic characteristics.

METHODS

We retrospectively evaluated 97 consecutive patients with a histological diagnosis of cirrhosis and preserved liver function, enrolled in a surveillance program for early diagnosis of HCC. Hepatocyte proliferation was evaluated by flow-cytometric analysis in liver samples collected at the time of histological diagnosis of cirrhosis. All patients were followed with abdominal US and serum alpha-fetoprotein (AFP) assays every 6 months.

RESULTS

During a mean follow-up of 53 months (range, 12-120 months), 12 patients developed HCC, giving an annual incidence of 2.8%. The mean S-phase fraction was 2.5%+/-1.6 in patients who developed HCC and 0.9%+/-0.6 in those who did not (p < 0.0001). By univariate analysis, S-phase fraction 1.8% or higher and AFP higher than 20 ng/ml were the only two variables significantly correlated with the development of HCC (p < 0.0001, p < 0.0001). Multivariate analysis found that both variables were independently associated with HCC development (p < 0.003 and p < 0.005, respectively), with hazard ratios of 8.0 and 7.3 (confidence intervals, 2.1-31.2 and 1.8-29.2). Among patients with high AFP and/or high S-phase fraction, 11 (39%) developed HCC, compared with only one (1%) with a low S-phase fraction and normal AFP, corresponding to HCC yearly incidences of 9.5% and 0.3% (p < 0.00009).

CONCLUSIONS

Patients with high S-phase fraction and/or above-normal serum AFP are at higher risk of developing HCC and should be offered a close surveillance program.

Flow cytometric DNA analysis and p53 protein expression show a good correlation with histologic findings in patients with Barrett's esophagus

BACKGROUND

There is a considerable degree of subjectivity and, therefore, substantial interobserver and intraobserver disagreement in the diagnosis and grading of dysplastic lesions in Barrett's esophagus (BE). The aim of this study was to evaluate the usefulness of DNA flow cytometry and immunohistochemical staining for p53 protein as objective methods to complement the conventional histologic diagnosis of dysplasia in patients with this disease. The most common problems and the possible advantages of using these procedures are analyzed briefly in this article.

METHODS

Formalin fixed, paraffin embedded tissue from 55 patients diagnosed with BE were processed for flow cytometric measurements (ploidy and proliferation index) and p53 immunostaining.

RESULTS

Both the cytometric data and the positivity of staining for p53 revealed a statistically significant increase throughout the following sequence: no dysplasia --> indefinite for dysplasia --> low grade dysplasia --> high grade dysplasia --> adenocarcinoma. There was also a highly significant correlation between the results of the cytometric study and the positivity of staining for p53.

CONCLUSIONS

In the future, the use of this procedure could play an important role in the evaluation of patients with BE. Considering that staining for p53 is technically simple, economical, and quick, and the materials required are available to most pathology laboratories, this method appears to be a firm candidate for application as a biomarker in BE. The authors have shown that it is possible to obtain adequate results for cytometric analysis with small formalin fixed, paraffin embedded biopsies if a strict protocol for the acceptance of tissue samples and/or histograms is observed.

Flow cytometric DNA ploidy and S-phase fraction correlate with histopathologic indicators of tumor behavior in colorectal carcinoma

BACKGROUND

The clinical behavior of colorectal carcinoma is highly variable without reliable predictive biomarkers. Previous reports have shown that flow cytometric DNA analysis may provide valuable prognostic information in these tumors.

PURPOSE AND METHODS

This study evaluates the DNA ploidy and the S-phase fraction (SPF) on frozen samples obtained from 61 patients with colorectal carcinoma by using flow cytometry, and it correlates the data with histopathologic features known to affect disease prognosis. Tumors were classified using the World Health Organization's histologic criteria and were staged according the American Joint Committee on Cancer's classification system. Grade of the neoplasm, vascular invasion, and perineural tumor spread were evaluated in every case.

RESULTS

Fifty-nine percent of tumors were aneuploid and showed statistically significant higher S-phase values than diploid tumors (22.5 vs. 11.2 percent; P < 0.00001). Mean SPF of the whole series was 17.9 (range, 4.2-44.2) percent. A statistically significant association was found between SPF values and histologic grade (P < 0.0016), nodal status (P < 0.0007), distant metastasis (P < 0.0001), tumor stage (P < 0.0001), venous invasion (P < 0.0002), and lymphatic permeation (P < 0.01) but not with perineural growth and infiltration of the neoplasm through the bowel wall (T). DNA ploidy correlated positively with tumor stage (P < 0.03), and the association between aneuploidy and advanced stages of the disease was statistically significant.

CONCLUSIONS

These findings showed that flow cytometric DNA ploidy and SPF, evaluated in fresh samples, are potentially useful parameters to estimate colorectal carcinoma biopathology. Aneuploidy and high replicative neoplastic activity correlated with histopathologic features that are commonly associated with the prognosis of colorectal carcinoma, being SPF-related to disease dissemination and, therefore, an indicator of clinical relevance.

Prognostic impact of proliferation-associated factors MIB1 (Ki-67) and S-phase in node-negative breast cancer

MIB1 proliferation rate (MIB1-PR) and total S-phase fraction (SPF) were retrospectively determined in formalin-fixed, paraffin-embedded sections of 90 primary node-negative breast carcinomas. None of the patients had received adjuvant systemic therapy. Median follow-up in patients still alive at the time of analysis was 37.5 months (16-72 months). Immunostaining of Ki-67 antigen was performed using the monoclonal antibody MIB1 and the APAAP technique. An adjacent 50-microm paraffin section was used for flow cytometric S-phase determination. Results were compared to established clinicopathological prognostic factors. MIB1-PR was significantly correlated to grading (P = 0.018); SPF was significantly correlated with tumour size (P = 0.041) and inversely with steroid hormone receptor status (P = 0.03). A significant correlation between MIB1-PR and SPF was found in aneuploid (P = 0.025) but not in diploid tumours (P = 0.164). In univariate analysis, both MIB1-PR (optimized cut-off of 25%) and SPF (optimized cut-off of 8%) were significant prognostic factors for disease-free survival (DFS) (MIB1-PR, P = 0.0224; SPF, P = 0.0028). In multivariate analysis, however, only SPF remained significant; it was the strongest prognostic factor for DFS (P = 0.0073), stronger than MIB1-PR or established clinicopathological prognostic factors. We thus conclude that MIB1-PR and SPF provide additional prognostic information in node-negative breast cancer. However, in our study, flow cytometrically determined SPF had the greater prognostic impact.

S-phase fraction identifies high-risk subgroups among DNA-diploid breast cancers

The prognostic value of DNA content measured by means of flow cytometry was analyzed in formalin-fixed, paraffin-embedded samples from 231 breast cancer patients treated between 1984 and 1988, with a mean follow-up period of 55 months. We followed the guidelines of a Consensus Meeting held on this issue in Maine, USA, in 1992. DNA-diploid and -aneuploid tumors were evaluated separately for the fraction of cells in S-phase (SPF) contained in them, this being divided into three groups ('high', 'intermediate', and 'low'), defined by the 25th and 75th centile of the SPF-distribution corresponding to either DNA-diploid or DNA-aneuploid tumors. Unequivocally readable histograms were obtained from 174 samples (75.3%). A high SPF in diploid tumors was significantly associated with a higher recurrence rate (p = 0.015), a shorter disease-free survival (p = 0.014), advanced (IIIB) clinical stage (p = 0.034), and almost significantly with total survival (p = 0.055). In a multivariate Cox regression analysis, a high SPF in diploid tumors retained its independent prognostic power, being significantly associated with a shorter disease-free survival (p = 0.00049) and total survival (p = 0.0077). It also allowed to identify a subgroup with an ominous prognosis among patients < or = 50 years of age with early stage tumors. Our results fully validate the recommendations of the 1992 Maine Consensus Meeting.

Image cytometric analysis in pathology

Image cytometry (ICM) is used in surgical pathology to quantify nuclear DNA content, nuclear and cytoplasmic immunostain. DNA aneuploidy is shown to be an independent negative prognostic factor in malignant melanoma, small cell carcinoma of the lung, esophageal, ovarian, endometrial, prostatic, urinary bladder, and papillary thyroid carcinoma. On bladder washings, DNA ploidy by ICM is used as an aid in diagnosis and management of recurrent transitional cell carcinoma of the bladder. Quantitation of nuclear immunostain for proliferation markers by ICM has clinical significance in prognosis and management of solid tumors of bladder, breast and ovary, astrocytoma, lymphoma, and malignant melanoma. Angiogenesis, measured by microvessel density is a predictor of prognosis in breast carcinoma and an independent predictor of metastasis for breast carcinoma, malignant melanoma, non-small cell lung carcinoma, and prostate carcinoma. Quantitated by ICM, angiogenesis is predictive of the presence or subsequent development of regional lymph node metastases in head and neck squamous carcinomas. Future prospects for ICM in pathology include the standardization of ICM techniques; extended clinical use of DNA ploidy for diagnosis, prognosis and as a help with therapeutic decisions; development of neural networks and quantification of fluorescence in situ hybridization to distinguish benign from malignant lesions of low malignant potential, and three-dimensional reconstruction of morphology from two-dimensional sections measured for prognostic parameters.

Debris compensation of DNA histograms and its effect on S-phase analysis

Debris compensation is an important variable affecting S-phase fraction (SPF) analysis in flow cytometric DNA histograms. The SPF was estimated in fresh frozen breast carcinomas using the following four debris subtraction algorithms: modeling debris as an exponential curve (EXP); the incorporation of nuclei cut a single time into the exponential moel (EXP-SC); the random cutting of nuclei into multiple pieces of varying sizes (MC); and a combination of both nuclear cutting models (SC-MC). Comparison of SPF estimates indicated that the various debris subtraction models yielded differences in SPF, with SPF values obtained using the exponential model having considerable variation compared to SPF estimates from histograms where debris was modeled by algorithms based on nuclear slicing and fragmentation. However, SPF estimates could be affected by initial placement of the nuclear debris boundaries, the coefficient of variation of the G0/1 peak, and the relative amount of debris. Using the ratio of the height of the G0/1 peak to the height of the debris between the chicken red blood cells (CRBC) and G0/1 peaks as an objective measurement of nuclear debris, debris compensation was necessary in diploid DNA histograms where this ratio was as low as 1.5%. Taken in the context of SPF prognostic cutoff levels, variation in debris models and boundaries can change the classification of cases with borderline SPF levels into the poor prognostic high SPF categories, thereby making the comparison of SPF values derived from different studies difficult.

DNA ploidy and the percentage of cells in S-phase as prognostic factors for women with lymph node negative breast cancer

BACKGROUND

Previous cell kinetic studies have shown that the percentage of cells in S-phase (%S) of the tumor may be an important prognostic factor for relapse-free survival (RFS) and overall survival (OS) in patients with resected lymph node negative breast cancer.

METHODS

This study examined DNA ploidy and %S from the paraffin embedded primary tumors of 265 patients who had surgery between 1975 and 1981, had lymph node negative cancer, and had no adjuvant therapy. The %S and %G2M values were calculated using a debris and aggregate subtraction model.

RESULTS

The results of the DNA ploidy analysis revealed 130 (49%) DNA diploid tumors and 135 (51%) DNA nondiploid tumors. Ploidy was not significant for either RFS (P = 0.20) or OS (P = 0.13). The total %S (using a cutoff of 8%) was a statistically significant prognostic factor for RFS (P = 0.003) and borderline for OS (P = 0.08). The proliferation fraction (%S + %G2M), using a cutoff of 12.5, was a statistically significant prognostic factor for RFS (P = 0.01) and for OS (P = 0.01). In a Cox multivariate analysis for RFS, the total %S remained significant (P = 0.05) along with tumor size. In the analysis of OS, the proliferation fraction remained significant (P = 0.03) along with tumor size and age. DNA ploidy was not significant in any multivariate analysis.

CONCLUSIONS

This study suggests that tumor size and cell proliferation parameters are independent prognostic factors for patients with resected lymph node negative breast cancer. However, the clinical usefulness of the cell kinetic parameters appears limited.

Use of the mitotic counts for the prognosis and grading of breast cancer. Method evaluation study

Reproducibility of the volume fraction-corrected mitotic index (M/VV index) was studied in 144 unselected breast cancer specimens. The influence on decision making of variation in determining the index was also analysed. In the complete series of specimens the correlation between two observers, one subjectively estimating the epithelial fraction of tumor epithelium and the other using point-counting (10 x 10 ocular grid), was good (Pearson's r = 0.82, p < 0.001, 95% CI 0.70-0.92). A subset of 30 specimens was used to evaluate the grading efficiency (GE) of the M/VV index method. The mean grading efficiency as estimated from this subset varied between 90% and 93%. The average minimum GE value was 82.8% (SD = 3.4%). The findings suggest that when the M/VV index method is used, the grading is correct on average in 90% or more of the cases, but dependent on the cutoff point. The over-all grading efficiency of the M/VV index method was comparable to that obtained from published S-phase fraction data on breast cancer specimens from three independed laboratories. We conclude that the M/VV index in breast cancer analysis is a sufficiently reproducible method in mitosis counting, and that it can be used with subjective or point count estimation of the area fraction of neoplastic epithelium.

Clinical significance of DNA ploidy and S-phase fraction and their relation to p53 protein, c-erbB-2 protein and HCG in operable muscle-invasive bladder cancer

DNA ploidy and S-phase fraction (SPF), determined by flow cytometry were studied in 118 patients with muscle-invasive transitional cell carcinoma (TCC) of the urinary bladder, scheduled for cystectomy after pre-operative radiotherapy (20 Gy/1 week) with or without systemic cisplatin-based neo-adjuvant chemotherapy. The correlation between these parameters and immunohistochemically demonstrated p53, c-erbB-2 and HCG was also investigated. There were 16 DNA diploid and 102 DNA non-diploid tumours. DNA ploidy was not related to the T (all 118 patients) or pN (58 patients) category, occurrence of stage reduction or cancer-related 5 years survival. Patients with high SPF tumours tended, however, to have a better prognosis than those with low SPF TCC reaching the level of significance (P < 0.05) for those patients who had high SPF tumours and received neo-adjuvant chemotherapy. Fifty-one of the tumours were p53 positive. p53 positive tumours were significantly more often found in TCC with low SPFs than in those with high SPFs. Respectively 12 and 9% of the tumours were HCG and c-erbB-2 positive, without correlation to DNA ploidy or SPF. We conclude that DNA ploidy does not represent a prognostic parameter in muscle-invasive operable bladder carcinomas. A high SPF, determined by FCM, may be helpful to identify patients with chemotherapy-sensitive TCC of the urinary bladder.

Flow cytometry and Zollinger-Ellison syndrome: relationship to clinical course

BACKGROUND

With successful means of controlling gastric acid secretion in patients with Zollinger-Ellison syndrome, the gastrinoma itself is becoming the major determinant of long-term survival. No methods have yet been described to predict which tumors will have more malignant courses thereby indicating which patients should undergo aggressive surgery or antitumor therapy. Because DNA analysis, using flow cytometry, has proved helpful in this regard in other tumors, the current study was designed to evaluate its utility in gastrinoma patients.

METHODS

Flow cytometry was performed on 81 paraffin-embedded gastrinoma specimens from 59 patients. Results were compared with preoperative patient characteristics, findings at surgery, and postoperative follow up.

RESULTS

Tumors were diploid in 54% of patients, near diploid in 15%, pure tetraploid in 0%, nontetraploid aneuploid in 25%, and multiple stem line aneuploid in 5%. All patients with multiple stem line aneuploid tumors had wide-spread metastases whereas all patients with nontetraploid aneuploid tumors had localized or regional disease. Median S phase percentage was 3.6. S phase percentages were higher in patients with widespread metastatic disease than in patients with localized or regional disease. Disease extent also correlated closely with fasting serum gastrin level. After removing this variable with logistic regression analysis, the significant correlation between disease extent and DNA analysis persisted.

CONCLUSIONS

DNA analysis of gastrinoma tissue specimens correlates independently with the extent of disease and may be useful in planning therapeutic strategies for patients with Zollinger-Ellison syndrome.

Ductal carcinoma of breast: nuclear grade as a predictor of S-phase fraction

Nuclear grade (NG) and S-phase fraction (SPF) are established independent prognostic variables for ductal breast carcinomas. Nuclear grade can be assigned by a pathologist in a simple fashion during histopathologic evaluation of the tumor, while SPF requires flow cytometric evaluation of tumor samples. This prospective study was undertaken to determine whether elevated SPF could be predicted from NG alone and how NG and SPF correlate with c-erbB-2 expression. Eighty-two breast carcinomas of ductal type were assigned an NG of low (grade 1 or grade 2) or high (grade 3). S-phase fraction was recorded initially from fresh-frozen tissue samples and was designated as either low SPF (below the value designated as the cutoff for elevated SPF) or high SPF (a value at or greater than the cutoff value). On fresh tissue the NG predicted the range of SPF (low or high) in 89% of cases. Four percent of the cases that did not correlate could definitely be attributed to sample error. The remaining 7% that did not correlate could have been due to sample error, specimen quality, or tumor heterogeneity, as demonstrated by reversal of SPF range as performed on paraffin blocks of tumor. Eighty-eight percent of the tumors positive for c-erbB-2 were NG 3 and 12% were NG 2. All c-erbB-2 tumors were aneuploid. This study demonstrates the importance of carefully assigning NGs on tissue and indicates the importance of reviewing flow cytometric data side by side with histopathologic parameters to detect discrepancies between these two modalities. Careful nuclear grading assignment can accurately predict the range of SPF.

Immune stimulation by an antisense oligomer complementary to the rev gene of HIV-1

Mice developed massive splenomegaly and polyclonal hypergammaglobulinemia within 2 days after intravenous injection of a phosphorothioate oligomer that is antisense to a portion of the rev region of the HIV-1 genome. Histologic examination of spleens from injected animals showed marked expansion of a uniform-appearing population of small lymphocytes and many mitoses. Spleen mononuclear cells (SMNCs) from injected animals showed approximately a 10-fold-increased uptake of [3H]thymidine and production of IgM and IgG. Flow cytometry analysis indicated that the responding cells were predominantly B-lymphocytes. The anti-rev oligomer also was mitogenic in vitro and stimulated immunoglobulin production by normal mouse SMNCs and human peripheral blood mononuclear cells. Similar immunologic effects were observed with an anti-rev 21-mer phosphorothioate, truncated at the 3' end, but not with a 20-mer human p53 antisense phosphorothioate or a 28-mer anti-rev phosphodiester. These observations are consistent with the possibility that DNA sequences homologous to the rev gene participate in the regulation of mammalian lymphocyte activation, proliferation and maturation.

DNA signal splitting improves detection and analysis of tetraploid populations

Detection of DNA tetraploid populations requires a high index of suspicion at the time of data acquisition and frequently requires subsequent off-line analysis for confirmation, including evaluation of the hypertetraploid region. To analyze these specimens, the flow cytometer operator must run all specimens with the G0G1 peak in low channels or rerun specimens in which tetraploidy is suspected with a lower photomultiplier tube (PMT) voltage or lower amplifier gain setting. Re-analysis may not be possible in specimens with few cells. A simple modification to the cytometer allows PMT signal splitting with simultaneous processing of the signal by two different amplifiers. This allows simultaneous acquisition of histograms optimized for both the hypotetraploid and hypertetraploid regions.

Improved prognostic impact of S-phase values from paraffin-embedded breast and prostate carcinomas after correcting for nuclear slicing

Nuclear debris may significantly interfere with the analysis of S-phase fraction (SPF) from paraffin-embedded tumors. We used a background subtraction algorithm to compensate for the effects of slicing of tumor cell nuclei during preparation of paraffin-embedded specimens. DNA histograms were analyzed from 88 node-negative breast and from 78 prostatic carcinomas. Median SPFs corrected for nuclear slicing were lower than uncorrected ones in both breast cancer (7.6% vs. 5.7%) and prostate cancer (6.7% vs. 4.2%). The median SPF value in each group was used as a cut-off point in survival studies. As compared with the uncorrected SPFs, corrected SPF levels resulted in a more significant survival difference between breast cancer patients with above and below median SPF (p = 0.0014 vs. p = 0.014) and in a higher relative risk (RR) of death (4.5 vs. 3.1). The same was true for prostate cancer survival (p less than 0.0001 vs. p = 0.002) and RR (5.3 vs. 3.1). Compared with the exponential background subtraction method, the sliced nuclei correction was more reproducible and could be applied in all evaluable histograms without the risk of overcompensation. In conclusion, our results support the use of background correction with the sliced nuclei model in DNA flow cytometric studies of archival tissues.