2.1

Sample size calculation

The estimated sample size (n = 100 patients) was determined based on a prevalence rate of 63% for lymph-node metastasis, a per-patient sensitivity of 100%, and a specificity of 72.75% with a confidence interval of ± 0.15 for specificity, as per our previous publication [ ]. This calculation also accounted for an anticipated dropout rate of 5% [ ]. Approximately 35–40 patients with carcinoma penis undergo penectomy with lymph-node dissection at our institute per year. The study was conducted between January 1, 2020, and December 31, 2023, to achieve the desired sample size. All the patients with carcinoma of the penis who presented at our institute during the study period and fulfilled the inclusion criteria were included in the study.

2.2

Inclusion and exclusion criteria

Inclusion criteria were age between 18 and 80 years, biopsy-proven squamous cell carcinoma of the penis, patients who presented primarily to our institute, patients who were not candidates for neoadjuvant chemotherapy, patients who did not opt for options other than surgery, and patients who consented to participation in the study. Exclusion criteria were histology other than squamous cell carcinoma, primary surgery done before presentation to our institute, patients with fixed inguinal nodes or involving skin, patients who presented with recurrence of primary surgery performed before the study period, metastasis on presentation, patients who were not fit for surgery, and patients who did not consent to participation in the study. Written consent for participation, analysis, and publication of the clinical data was obtained from all the patients.

2.3

Study design

On the initial visit, a thorough physical examination was conducted on each patient to record size (cm), site (glans/shaft) and the characteristics (ulcerative/exophytic) of the tumor along with palpation of inguinal lymph-nodes. The size of the lymph-nodes and loss of fatty hilum were noted on ultrasonography. MRI was used as an additional investigation for inguinal lymph-nodes in all cases. MRI was evaluated to address the heterogeneity amongst investigation protocol across various institutions. The size of lymph-nodes and irregular outline or the presence of necrosis was noted in MRI. The criteria of irregular outline/necrosis on MRI were adopted from previously published literature for other cancers [ ]. A wedge biopsy was performed and the type of tumor as well as mild, moderate or poor differentiation along with the presence or absence of LVI/PNI was recorded. Institutional pathologist reviewed the slides of external biopsy report. CRiSS score (0–9) was calculated and group (low/intermediate/high risk) was assigned to all patients.

After a well informed and written consent, all included patients were subjected to primary surgery (partial/total penectomy) and bilateral radical inguinal lymph-node dissection. Partial or total penectomy was performed depending on the feasibility. The radical inguinal lymphadenectomy was performed as described by Daseler et al [ ]. The final histopathology report was recorded and correlated with CRiSS score and groups. Pathological T stage, N stage and the number of dissected lymph-nodes were noted. USG was done by the same team of 2 radiologists throughout the study period. Pathological analysis was done by the same team of experienced onco-pathologists. The radiologists and pathologists were both blinded to the clinical criteria. During the study period, the surgery was conducted by the same group of uro oncologists.

2.4

Statistical analysis

Descriptive analytics was used to quantify and describe the relationships between the selected variables and ILNM. Dichotomous variables were compared by Pearson’s Chi-square test with Yates continuity correction, and Fischer’s exact test was used if at least 1 cell of the table had an expected count smaller than 5. The association between the CRiSS score or groups and ILNM was tested through a logistic regression analysis (HR, 95% CI). The positive predictive value (PPV), negative predictive value (NPV), sensitivity, and specificity of the CRiSS score and groups were calculated. A 2 × 2 table is required for the calculation of sensitivity and specificity, but in cases where there are 3 test results, the result of the equivocal group can be omitted or it can be clubbed with lower or higher group for calculation [ ]. For the calculation of the sensitivity and specificity of each score, we combined the numbers of the rest of the scores to create a 2 × 2 table. The incidence of lymph-node metastasis was 55% (equivocal) in the intermediate CRiSS group; hence, they were grouped with high risk group for calculation of sensitivity and with low risk group for calculation of specificity. A 1-way ANOVA test was used to analyze the difference between the mean number of lymph-nodes dissected among the CRiSS scores and groups [ ]. A p-value of < 0.05 was considered statistically significant for the entire study. The statistical analysis was performed using the SPSS Statistics software for Windows (Version 25.0. Armonk, NY: IBM Corp.)

3.1

Patient characteristics

The characteristics of all the patients are presented in Table 2 . The median age of the patients was 57.45 years (40–75). Tumor larger than 3 cm was present in 38.4% (33 of 86 cases), of which 23 had ILNM. Seventy percent (29 of 41) of the patients had ILNM when they presented with ulcers. ILNM were predominantly found when the tumor was located in the shaft of the penis (73.3%). Inguinal lymph-nodes were palpable in 44 out of 86 (51.2%) patients. ILNM was present in 14 of 42 (33.3%) cases with non-palpable lymph-nodes and in 30 out of 44 patients (68.2%) with palpable lymph-nodes. Lymph-node size of more than 1cm on USG showed an ILNM rate of 70.5%, whereas it was 73.8% if there was a loss of fatty hilum. Ninety-one percent (11 out of 12) of patients with poorly differentiated primary tumors had ILNM, whereas 64.9% (24 out of 37) of patients with moderately differentiated tumors had ILNM. The presence of LVI or PNI could predict ILNM in 32 out of 38 (84.2%) patients. ILNM was found in 41.2%, 45.5%, 55.2%, and 85.7% of patients with T1, T2, T3, and T4 stages, respectively.

Table 2

Table showing patient characteristics of patients with and without ILNM

Parameters	Criteria	Total (n)	INLM absent	ILNM present	p-value
Size of tumor	<3cm	53	32	21	0.006
	>3cm	33	10	23
Characteristic of growth	Exophytic	45	30	15	0.001
	Ulcero-infiltrative	41	12	29
Extent of growth	Glans	41	30	11	0.001
	Shaft	45	12	33
Inguinal lymph node	Not palpable	42	28	14	0.001
	Palpable	44	14	30
Size of lymph nodes on USG	<1cm	42	29	13	0.001
	>1cm	44	13	31
Fatty hilum on USG	Preserved	44	31	13	0.001
	Lost	42	11	31
Size of lymph nodes on MRI	<8mm	41	28	13	0.001
	>8mm	45	14	31
Characteristics of lymph nodes on MRI	No Irregular outline/necrosis	42	29	13	0.001
	Irregular outline/necrosis	44	13	31
Grade	1	37	28	9	0.001
	2	37	13	24
	3	12	1	11
LVI/PNI	Absent	48	36	12	0.001
	present	38	6	32
T-stage	T1a	13	13	0	0.001
	T1b	4	1	3
	T2	33	22	11
	T3	29	10	19
	T4	7	1	6
Age	Mean (Years)	57.45	59.75	55.90	0.373

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