Perioperative Changes in Peripheral Natural Killer Cell Activity and Their Association With Clinicopathological Features in Breast Cancer: A Single‐Center Cohort Study

ABSTRACT

Objective

This study aimed to evaluate perioperative changes in peripheral blood natural killer (NK) cell activity (ACT) in patients with breast cancer and to investigate the relationship between NK activity and clinicopathological characteristics.

Methods

A single‐center retrospective cohort including 34 female patients with available preoperative and postoperative NK activity measurements was analyzed. Clinical and pathological variables were obtained from medical records. NK activity levels at two time points were compared, and the association between NK activity difference and age, tumor size, TNM stage, hormone receptor status, HER2 expression, Ki‐67 index, number of metastatic lymph nodes, and serum tumor markers was assessed. NK cell activity was assessed using the NK Vue assay (ATgen, Seongnam, Republic of Korea), a whole‐blood stimulation assay based on interferon‐gamma (IFN‐γ) release.

Results

Postoperative NK activity significantly increased compared with preoperative levels (p = 0.041). However, the change in NK activity was not significantly associated with tumor stage, lymph node involvement, tumor size, proliferation index, receptor status, HER2 expression, metastatic lymph node count, or serum tumor markers (all p > 0.05). The overall metastatic rate during follow‐up was low.

Conclusion

Surgical treatment appears to exert a favorable effect on peripheral NK cell activity in breast cancer. The absence of a clear correlation between NK activity changes and clinicopathological parameters suggests that NK responses may reflect an individualized immunologic capacity rather than tumor‐specific features. Larger prospective studies integrating NK cell subsets and functional phenotyping are required to better define the prognostic and predictive value of NK cell activity in breast cancer.

1. Introduction

Breast cancer is not only the most common malignancy in women worldwide, but also one of the leading causes of cancer‐related deaths [1]. Although advances in screening programs and systemic therapies have improved survival in recent years, the prognosis remains limited, particularly in metastatic and triple‐negative subtypes. Therefore, studies aimed at understanding tumor biology and the host immune response are becoming increasingly important.

Natural killer (NK) cells are an important effector component of the innate immune system. These cells have the capacity to recognize and eliminate tumor or virally infected cells without requiring prior antigen sensitization. They exert their cytotoxic effects through the perforin–granzyme pathway, death receptors (Fas–FasL, TRAIL), and cytokine release (particularly interferon‐γ, TNF‐α). Furthermore, NK cells interact with other immune cells and play a role in shaping the adaptive immune response. Recent evidence has highlighted the clinical relevance of NK‐cell–related parameters in breast cancer, with peripheral NK cell counts being associated with treatment response and prognosis in patients receiving neoadjuvant chemotherapy [2, 3].

The breast cancer microenvironment is in dynamic interaction with the immune system. The density and functional status of immune cells present in tumor tissue may be decisive in the course of the disease. In this context, studies on the distribution of tumor‐infiltrating NK (TINK) cells and circulating NK subgroups (e.g., CD56^bright^ and CD56^dim^ phenotypes) and activation/inhibition markers (NKG2D, NKp30, CD16, PD‐1, etc.) suggest that NK cell function may have prognostic value in terms of tumor progression and treatment response [2].

Research conducted over the past decade has revealed that NK cell activity is suppressed in advanced‐stage and particularly triple‐negative breast cancer cases, with immune‐suppressive cytokines such as TGF‐β and IL‐10 playing a role in this process. Furthermore, cancer‐associated fibroblasts and myeloid‐derived suppressor cells have been reported to reduce NK cell cytotoxicity. However, the detection of increased NK cell levels and elevated activation markers in some patients following chemotherapy or immunotherapy suggests that these cells may serve as biological indicators of treatment response [4].

NK cells may play a role not only in the direct elimination of tumors but also in the control of micrometastatic foci. Low NK cell activity has been shown to be associated with increased metastasis risk and poor clinical outcomes in different cohorts. These findings support the evaluation of NK cells as both a prognostic and potential therapeutic target [5].

Recent studies have demonstrated that peripheral NK‐cell–related parameters may have prognostic and predictive value in breast cancer patients receiving systemic treatment. Furthermore, the breast cancer tumor microenvironment contains multiple factors capable of suppressing NK‐cell function and contributing to immune escape. Therefore, evaluating perioperative changes in peripheral NK‐cell activity may provide insight into the dynamic interaction between tumor burden and host immune responses. In this context, the present study aimed to evaluate perioperative changes in NK‐cell activity and investigate their association with clinicopathological characteristics in breast cancer patients.

2. Materials and Methods

This study was designed as a single‐center, retrospective cohort study. All breast cancer patients who underwent surgical treatment at the University of Gaziantep between January 2023 and December 2023 were retrospectively screened through institutional medical records. Patients were eligible for inclusion if both preoperative and postoperative NK‐cell activity measurements were available. Cases with missing NK‐cell activity measurements at either time point or incomplete clinicopathological data were excluded. Because NK‐cell activity testing was not routinely performed in all breast cancer patients, the final study population consisted of 34 eligible patients meeting these predefined criteria.

Patient age, tumor side, tumor size, TNM stage, general stage, number of metastatic lymph nodes, ER/PR status, CerbB2 score, Ki‐67 index, and serum tumor markers (CEA, CA19‐9, CA15‐3, CA125) were obtained from electronic patient records. Tumor types were classified by reviewing preoperative and postoperative pathology reports.

2.1. Blood Collection and NK Cell Activity Assay Procedure

Peripheral venous blood samples were obtained from the antecubital region using a 19‐gauge butterfly needle attached to a sterile plastic syringe, ensuring uninterrupted venous flow. Approximately 15 mL of blood was collected, and the initial portion was discarded to minimize contamination. The remaining sample was promptly transferred into polypropylene tubes. Subsequently, samples were centrifuged at 3500 × g for 15 min at a controlled temperature range of 15°C–18°C. Following centrifugation, the plasma fraction was carefully separated and aliquoted into clean plastic tubes, then stored under appropriate conditions until further biochemical analysis.

2.2. Assessment of Natural Killer (NK) Cell Activity

NK cell activity was evaluated using a whole blood stimulation assay. Briefly, 1 mL of freshly collected whole blood was mixed with 1 mL of PROMOCA solution and incubated for 24 h at 37°C in a humidified CO₂ incubator. After incubation, samples were centrifuged and the supernatant was collected for cytokine analysis. Interferon‐gamma (IFN‐γ) release, indicative of NK‐cell activity, was quantified using the NK Vue assay (ATgen, Seongnam, Republic of Korea), a validated whole‐blood stimulation assay. IFN‐γ concentrations were expressed as pg/mL according to the manufacturer's instructions. For IFN‐γ measurement, standards and samples were added to microplates pre‐coated with anti‐human IFN‐γ antibodies and incubated for 2 h at room temperature. Plates were then washed four times using phosphate‐buffered saline containing 0.05% Tween‐20 (pH 7.4). Subsequently, an enzyme‐linked IFN‐γ detection conjugate was added and incubated for 1 h.

After seven washing steps, tetramethylbenzidine (TMB) substrate solution was introduced and allowed to react for 30 min. The enzymatic reaction was terminated using a stop solution, and optical density was measured spectrophotometrically at 450 nm. Preoperative and postoperative measurements were compared on an individual basis.

2.3. Statistical Analysis Method

1‐ Data Preprocessing: Data were evaluated for clinical consistency and potential outliers before analysis. No mathematical transformations or normalization procedures were applied to the raw data.

2‐ Data Presentation: Continuous variables (e.g., age, tumor size, and NK activity levels) are presented as mean ± standard deviation (SD), along with minimum and maximum values where appropriate. Categorical variables (e.g., tumor side, stage, ER/PR status) are expressed as frequencies and percentages (%).

3‐ Sample Size: The study included a total sample size of n = 34. All comparative analyses were conducted using this population.

4‐ Statistical Methods: The dependent samples t‐test was used to evaluate the difference between two dependent groups. The independent samples t‐test was used for comparisons between two groups, while one‐way analysis of variance (ANOVA) was used for comparisons between more than two groups. The relationships between quantitative variables and NK ACT levels were evaluated using Pearson correlation analysis.

5‐ The statistical analyses of the study were performed using IBM SPSS Statistics 26.0 software. The level of statistical significance was set at p < 0.05.

3. Results

All 34 patients listed in Table 1 are female. In terms of side distribution, 64.7% of patients had right breast involvement and 35.3% had left breast involvement. The highest rate in T staging is 88.2% at T2 level; T1 and T3 are equally represented (5.9%). In N staging, the most common group is N1 with 44.1%, followed by N2 (23.5%), N0 (20.6%), and N3 (11.8%). All patients were classified as M0 at initial diagnosis; metastatic events reported refer to outcomes observed during follow‐up. The highest rate in Stage distribution was observed in Stage 2B at 35.3%, while Stage 2A and 3A were 26.5% and Stage 3C was 11.8%. MRM (modified radical mastectomy) was performed on all cases. During follow‐up, 97.1% of the cases are alive, and 2.9% have died. There were no cases of local recurrence. In terms of metastasis distribution, 85.3% had no metastasis; 8.8% had bone metastasis, 2.9% had lung metastasis, and 2.9% had lung‐bone‐brain metastasis. In terms of blood group distribution, the most common group is O RH + at 35.3%, followed by A RH+(32.4%) and B RH + (20.6%); other blood groups are present at lower rates.

TABLE 1.

Frequency and percentage distributions of qualitative variables for the cases.

Qualıtatıve varıables	Groups	n	%
Sex	Female	34	100.0
Tumor side	Right	22	64.7
	Left	12	35.3
T category	T1	2	5.9
	T2	30	88.2
	T3	2	5.9
N category	N0	7	20.6
	N1	15	44.1
	N2	8	23.5
	N3	4	11.8
M category	M0	34	100.0
Disease stage	2A	9	26.5
	2B	12	35.3
	3A	9	26.5
	3C	4	11.8
Surgery performed	MRM	34	100.0
Survival status	Deceased	1	2.9
	Alive	33	97.1
Local recurrence	None	34	100.0
Metastasis during follow‐up	Lung	1	2.9
	Lung, bone, brain	1	2.9
	Bone	3	8.8
	None	29	85.3
Blood type	A RH+	11	32.4
	B RH+	7	20.6
	O RH+	12	35.3
	AB RH—	1	2.9
	B RH—	1	2.9
	O RH—	1	2.9

Abbreviations: MRM, modified radical mastectomy; RH, Rhesus factor.

The average age of the patients in Table 2 is 50.97, with the youngest individual being 27 and the oldest being 84 years old. The mean KI‐67 proliferation index is 36.82%, with values ranging from 5.0% to 90.0%. The mean estrogen receptor (ER) level is 57.03%, with a distribution ranging from 0% to 100%. The mean progesterone receptor (PR) level was 41.44%, with a minimum of 0% and a maximum of 95%. The mean number of metastatic lymph nodes was 4.56, with a minimum value of 0 and a maximum value of 33. The CerbB2 mean was determined to be 1.09; values ranged from 0 to 3. The mean tumor size was 26.41 mm, with a minimum of 6 mm and a maximum of 55 mm. Of the tumor markers, the mean CEA was 1.59 ng/mL (0.5–3.5), CA19‐9 was found to have an average of 9.02 U/mL (0.7–24.4), CA15‐3 had an average of 13.90 U/mL (1.4–31.9), and CA125 had an average of 11.46 U/mL (3.1–36.3).

TABLE 2.

Descriptive statistics of quantitative variables for patients.

Quantitative varıables	Mean	Sd	Min	Max
Age (Years)	50.97	11.31	27.0	84.0
Ki‐67 index (%)	36.82	28.41	5.0	90.0
ER‐Positive tumor cells (%)	57.03	41.40	0.0	100.0
PR‐ Positive tumor cells (%)	41.44	36.41	0.0	95.0
Metastatic lymph node count (Number)	4.56	7.82	0.0	33.0
HER2/CERBB2 IHC score (0–3)	1.09	1.31	0.0	3.0
Tumor size (mm)	26.41	11.06	6.0	55.0
CEA (ng/mL)	1.59	0.85	0.5	3.5
CA19‐9 (U/mL)	9.02	5.99	0.7	24.4
CA15‐3 (U/mL)	13.90	6.47	1.4	31.9
CA125 (U/mL)	11.46	6.52	3.1	36.3

Note: Data are presented as mean, standard deviation, minimum, and maximum values. Units of measurement are provided in parentheses for quantitative variables.

Abbreviations: CA, carbohydrate antigen; CEA, carcinoembryonic antigen; ER, estrogen receptor; HER2/CERBB2, human epidermal growth factor receptor 2; IHC, immunohistochemistry; PR, progesterone receptor; SD, standard deviation.

When preoperative diagnoses were evaluated in Table 3, 82.3% of cases were reported as invasive ductal carcinoma, 14.7% as invasive carcinoma, and 2.9% as invasive lobular carcinoma. In the postoperative pathology results, the invasive ductal carcinoma rate decreased to 73.5%, while the invasive carcinoma rate increased to 17.6%. The invasive lobular carcinoma rate was recorded as 5.9%, and additionally, a rare carcinoma type containing osteoclast‐like giant cells in the breast was identified in 2.9% of cases.

TABLE 3.

Distribution of preoperative and postoperative diagnoses.

Time	Diagnosis	n	%
Preoperative	Invasive ductal carcinoma	28	82.3
	Invasive carcinoma	5	14.7
	Invasive lobular carcinoma	1	2.9
Postoperative	Invasive ductal carcinoma	25	73.5
	Invasive carcinoma	6	17.6
	Invasive lobular carcinoma	2	5.9
	Carcinoma of the breast containing osteoclast‐like giant cells	1	2.9

Table 4 shows that NK ACT levels averaged 73.57 ± 172.33 pg/mL in the preoperative period, while this value rose to 408.59 ± 963.74 pg/mL in the postoperative period. The t‐value obtained in the comparison of dependent groups using the t‐test was −2.122, with p = 0.041. According to this result, the difference between preoperative and postoperative NK ACT levels is statistically significant (*p < 0.05).

TABLE 4.

Comparison of preoperative and postoperative NK ACT levels.

Variable	Preoperative, Mean ± SD	Postoperative, Mean ± SD	t	p
NK cell activity, IFN‐γ release (pg/ml)	73.57 ± 172.33	408.59 ± 963.74	−2.122	0.041 *

Note: Data are presented as mean ± standard deviation. Bold value indicates statistical significance (p < 0.05).

Abbreviations: NK, natural killer; SD, standard deviation.

^* p < 0.05.

In the analysis performed according to the side variable in Table 5, the mean NK ACT level (pg/mL) in the right breast was 280.15 ± 859.66, while this value was 396.94 ± 1120.31 in the left breast; the difference is not statistically significant (p = 0.736). When evaluated according to T Stage, the mean value was 3.60 ± 13.29 in T1 cases, 361.49 ± 1000.28 in T2, and 37.35 ± 57.49 in T3; the difference between groups was not significant (p = 0.804). In N staging, N1 cases had the highest mean at 633.65 ± 1367, while N0 was 110.24 ± 210.76, N2 was 79.04 ± 223.09, and N3 was 4.48 ± 53.16; the difference was not statistically significant (p = 0.412). The highest NK ACT level among the Stage groups was found in Stage 2B (791.73 ± 1497.33), with lower values in other stages; however, the difference between Stages was not statistically significant (p = 0.204). These findings indicate that there is no significant difference in NK ACT levels in terms of clinical variables.

TABLE 5.

Comparison of NK ACT levels according to clinical variables.

Variables	Groups	NK cell activity, IFN‐γ release (pg/mL), Mean ± SD	t	p
Tumor side	Right	280.15 ± 859.66	−0.340	0.736
	Left	396.94 ± 1120.31
T	T1	3.60 ± 13.29	0.220	0.804
	T2	361.49 ± 1000.28
	T3	37.35 ± 57.49
N	N0	110.24 ± 210.76	0.988	0.412
	N1	633.65 ± 1367
	N2	79.04 ± 223.09
	N3	4.48 ± 53.16
Disease stage	2A	86.54 ± 188.54	1.629	0.204
	2B	791.73 ± 1497.33
	3A	69.89 ± 210.48
	3C	4.48 ± 53.16

In Table 6, correlation analysis between NK ACT (pg/mL) difference and age, KI‐67, ER, PR, metastatic lymph node count, CerbB2, tumor size, CEA, CA19‐9, CA15‐3, and CA125 levels revealed no statistically significant relationship for any variable (p > 0.05). The highest positive correlation was observed with CA125 level (r = 0.253), but this relationship did not reach statistical significance (p = 0.156). Weak and insignificant negative correlations were reported between the NK ACT difference and all other variables. These results indicate that the clinical and biochemical variables evaluated in the study are not significantly related to changes in NK ACT levels.

TABLE 6.

Correlation between quantitative clinical and biochemical variables and NK ACT level difference.

Quantitative variables		Change in NK cell activity, IFN‐γ release (pg/mL)
Age (years)	r	−0.102
	p	0.567
KI‐67 Index (%)	r	−0.014
	p	0.938
ER‐Positive tumor cells (%)	r	−0.017
	p	0.925
PR‐Positive tumor cells (%)	r	−0.086
	p	0.628
Metastatic lymph node count (number)	r	−0.133
	p	0.455
HER2/CERBB2 IHC score (0–3)	r	−0.048
	p	0.788
Tumor size (mm)	r	−0.150
	p	0.397
CEA (ng/mL)	r	−0.013
	p	0.942
CA19‐9 (U/mL)	r	−0.192
	p	0.292
CA15‐3 (U/mL)	r	−0.170
	p	0.336
CA125 (U/mL)	r	0.253
	p	0.156

Note: r represents the correlation coefficient.

Abbreviations: CA, carbohydrate antigen; CEA, carcinoembryonic antigen; ER, estrogen receptor; HER2/CERBB2, human epidermal growth factor receptor 2; IHC, immunohistochemistry; NK, natural killer; PR, progesterone receptor.

4. Discussion

In this study, peripheral NK cell activity was evaluated in 34 patients who underwent surgery for invasive breast cancer in the preoperative and postoperative periods, and a significant increase in NK ACT levels was detected after surgery. However, no significant association was found between NK ACT changes and clinical‐pathological variables such as age, tumor size, lymph node status, histological diagnosis, hormone receptors, HER2 status, Ki‐67, tumor markers, and side. These findings support the heterogeneous results in the literature regarding the prognostic role of NK cells in breast cancer.

Numerous studies have demonstrated that NK cells in breast cancer are functionally suppressed both in the tumor microenvironment and in peripheral blood, with decreased activation receptor expression and impaired function due to immunosuppressive cytokines (TGF‐β, IL‐10, PGE₂, etc.) Gulić et al. emphasized that despite the antitumor potential of NK cells in breast cancer, their cytotoxicity is often reduced due to the chronic inflammatory and immunosuppressive environment in the tumor microenvironment, and that this suppression may be related to treatment response and clinical outcomes [3]. Abdel‐Latif and Youness suggest that NK cell‐based immunotherapies may serve as an alternative or complementary strategy to classical checkpoint inhibitors in triple‐negative breast cancer [6].

Studies examining the relationship between NK cell infiltration in tumor tissue and prognosis complement the activity results we measured in peripheral blood. Bouzidi et al. demonstrated that patients with high CD56‐defined tumor‐infiltrating NK (TINK) cell density had better overall and disease‐free survival despite more aggressive pathological features. Liu et al. reported that a risk model composed of NK cell‐related genes in triple‐negative breast cancer could predict both survival and immunotherapy response [7]. These data suggest that not only the presence of the NK system, but also its functional status and genetic signature may be important in terms of clinical outcomes.

Recent evidence suggests that NK cells in breast cancer should not be interpreted as a homogeneous immune population. Tumor‐associated NK cells, circulating NK cell subgroups, and NK‐related gene signatures may show different associations with tumor subtype, immune escape, treatment response, and prognosis. In particular, the functional suppression of NK cells within the breast cancer tumor microenvironment, mediated by stromal components, immunosuppressive cytokines, and altered activation/inhibition receptor signaling, may partly explain the variability in NK cell–related clinical findings across different cohorts [8, 9, 10, 11].

In our study, preoperative NK ACT levels were within a range consistent with the decrease in peripheral NK function in breast cancer patients described in previous series. In addition to classic studies reporting decreased NK activity in patients with early and advanced breast cancer compared to healthy controls, a more recent study by Piroozmand et al. reported that NK activity was low in breast cancer patients before treatment but showed a significant increase after systemic treatment [12]. Similarly, Verma et al. showed that peripheral NK cell profiles partially improved after neoadjuvant chemotherapy and surgery in patients with large and locally advanced breast cancer, particularly in those who achieved a pathological complete response [13]. The significant increase in NK ACT levels after surgery, which was also observed in our series, can be explained by the partial regression of the immunosuppressive tumor microenvironment and the rebalancing of the systemic immune response following the removal of the tumor mass.

However, in our study, no significant relationship was found between NK ACT difference and prognostic indicators such as tumor stage, lymph node involvement, hormone receptors, HER2 status, and Ki‐67. N'Da Marcelin et al., who evaluated NK cell concentration in peripheral blood, also reported that NK cell counts in breast cancer patients did not show a significant relationship with tumor stage, immunohistochemical subtype, or type of treatment administered [14]. This suggests that peripheral NK cell measurements may not be sufficiently sensitive on their own to reflect tumor biology and prognosis, especially in studies with limited sample sizes.

On the other hand, the relationship between NK cell infiltration in tumor tissue and aggressive subtypes presents a different picture. Bouzidi et al. showed that high CD56+ NK infiltration was associated with HER2‐positive and triple‐negative subtypes, high SBR grade, and high Ki‐67, but nevertheless, survival was better [7]. This finding suggests that the presence of NK cells in the tumor bed may indicate cases where the host can develop an effective immune response despite the tumor being biologically more aggressive. As emphasized by Gulić et al., different NK subpopulations (CD56^bright^, CD56^dim^, etc.) in breast cancer play different functional roles both within the tumor and in the periphery, and this heterogeneity complicates clinical correlations [15]. The fact that only total NK activity was evaluated in our study may have contributed to the inability to detect subpopulation differences and to the difficulty in establishing a relationship with clinical variables.

Experimental studies focusing on the effect of NK cells on metastasis and cancer stem cells support the clinical significance of the increase in NK activity after surgery. Tallerico et al. demonstrated that NK cells control the hematological spread of cancer stem cells associated with breast cancer and that NK activation can limit metastatic spread [16]. Coënon et al. reported that NK cells are at the forefront of the tumor‐immune microenvironment in solid tumors and are key effectors directing immune activation [17]. Due to the very limited number of metastatic events (n = 5) in our study, a formal statistical comparison was not feasible. Although limited by the small number of metastatic cases, exploratory observations did not suggest a clear pattern between NK activity changes and metastasis development; however, this warrants investigation in larger cohorts. When these findings are considered together, it can be thought that the increase in NK activity after surgery may be critical not only for the removal of macroscopic tumor burden but also for the immune surveillance of possible micrometastatic foci. However, since long‐term metastasis and survival data were limited in our study, it was not possible to determine the true prognostic significance of the increase in NK ACT.

In recent years, immunotherapeutic approaches targeting NK cells (ex vivo activation/expansion, patient selection based on NK cell‐associated gene signatures, CAR‐NK strategies, etc.) have been reported to be gaining increasing importance [6]. In light of these developments, monitoring pre‐ and postoperative NK activity in breast cancer may help predict which patients are likely to benefit most from NK‐based approaches. Our findings suggest that postoperative NK function can recover at least in the short term, but this recovery does not directly correlate with tumor stage or classic prognostic indicators.

4.1. Limitations

Our study has some limitations. First, its single‐center nature and relatively small sample size (n = 34) limit its statistical power and make it difficult to detect significant associations, particularly in subgroup analyses. Given the limited sample size, subgroup and correlation analyses should be interpreted as exploratory and hypothesis‐generating rather than definitive. No adjustment for multiple comparisons was performed due to the exploratory design and limited sample size; therefore, the findings should be interpreted with caution. Second, NK activity was assessed only in peripheral blood and at two time points; NK infiltration in tumor tissue and subpopulation distributions were not examined. Third, the absence of a healthy control group precludes direct comparison of NK ACT levels with the normal population. Finally, because treatment regimens and timing (chemotherapy, hormone therapy, etc.) were not fully standardized, the potential effects of these treatments on NK function could not be analyzed in detail. Furthermore, because NK‐cell activity testing was not routinely performed in all eligible breast cancer patients, selection bias cannot be completely excluded.

Despite all these limitations, our study suggests that surgical treatment may have a positive effect on peripheral NK cell activity and indicates that the NK cell response is a dynamic parameter reflecting not only tumor burden but also host‐specific immune capacity.

5. Conclusion

This study demonstrates that surgical treatment in breast cancer leads to a significant increase in peripheral NK cell activity. Our findings suggest that NK cell activity may reflect individual immune dynamics following surgery; however, no direct association with prognostic clinical parameters was demonstrated. To determine the true prognostic and predictive value of NK cells, prospective studies with larger sample sizes, including NK subpopulation distribution and functional markers, are needed.

Author Contributions

Mehmet Ali Melik: conceptualization, writing – original draft. Alper Aytekin: methodology, project administration. Ersin Borazan: writing – review and editing, formal analysis. Muhsin Elçi: visualization, validation.

Ethics Statement

This study received approval from the institutional ethics committee (Approval No: 2022/2023, Date: 26.10.2022). The requirement for informed consent was waived due to the retrospective design of the study.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data supporting this study are available from the corresponding author upon reasonable request. Due to institutional regulations and patient confidentiality, raw data cannot be publicly shared.