Materials and Methods

Data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) Registry from vulvar cancer cases diagnosed between 1973 and 2009 were the source for this analysis. Because all information from the SEER Program data is deidentified, informed consent by the study participants and approval of an ethics committee were unnecessary to perform the analyses in this study.

The SEER Program collects high-quality data on cancer-related variables pertaining to cancer incidence, cancer mortality, and cancer survival. Eligible women were older than 18 years with newly histologically confirmed squamous cell carcinoma of the vulva. Women who were not AA or white, women who were diagnosed by death certificate or at autopsy, or women with a previous diagnosis of malignant cancer were excluded.

The SEER Public Use Data include SEER incidence and population data grouped by age, sex, race, year of diagnosis, and geographic area and provide information regarding stage of disease; tumor grade, size, and histology; lymph node status; and overall survival for each registered patient.

Variables were coded according to SEER Program criteria. The exposure variable, race, was designated as whites and AA. Marital status was categorized as married, not married, and unknown. Geographic location was divided into the 9 SEER locations. Tumor grade was classified as well differentiated, moderately differentiated, poorly differentiated, undifferentiated, or unknown.

We used the SEER Summary Staging (localized, regional, and distant) to categorize the extent of the disease. The primary treatment modality (radiation, surgery, or no treatment) was also recorded. The outcome variables included the vital status and the time to event from the date of the diagnosis until death, censoring, or the last follow-up, as verified by the SEER Program vital status determination. Among the deceased persons listed in the SEER Registry, death may have occurred from vulvar cancer or any other cause of death, and this factor was analyzed separately.

Results

The SEER dataset included 396,386 women who were diagnosed with reproductive cancer within the SEER 9 registries from 1973 to 2009, of whom 7341 were diagnosed with squamous vulvar cancer. A total of 1474 patients were excluded from the final analysis: 228 cases because of race (not white or AA), 1 case because of age (younger than 18 years old at diagnosis), 1224 cases who had a prior malignancy, and 21 cases that were not microscopically confirmed. The final study group consisted of 5867 women, 5379 whites (91.6%), and 488 AA (8.3%).

Table 1 summarizes the demographic and clinical characteristics of the study population. The mean age at diagnosis was 57 years for AA and 67 years for whites ( P < .001). AA were less frequently married at the time of diagnosis (25.6% vs 38.3%; P < .001). AA had a lower rate of localized disease (60% vs 62.6%) and higher rate of regional (29.7% vs 28.7%) and distant metastasis (6.1% vs 3.7%) ( P = .04). AA had a lower rate of well-differentiated cancer (17.4% vs 27.8%; P < .001). Primary treatment was also significantly different between the groups: AA had surgery less frequently (84.2% vs 87.6%; P = .03); however, they frequently had more radiotherapy (24.2% vs 20.6%; P < .001). Lymph node metastasis of the tumor was not significantly different between the groups; however, we encountered substantial proportion of unknown data.

In the crude models for both all-cause mortality and cancer-specific mortality, AA had a decreased overall and disease-specific hazard of death compared with white women ( Table 2 ). The overall HR for AA women was 0.84 (95% CI, 0.74–0.95), and the disease-specific HR was 0.66 (95% CI, 0.53–0.82). Table 2 presents the risk of mortality for AA compared with whites, stratified by decade. AA women had a significant lower HR of vulvar cancer related mortality in the periods of 1990-1999 (HR, 0.56; 95% CI, 0.37–0.83) and 2000-2009 (HR, 0.65; 95% CI, 0.43–0.97). The Figure demonstrates Kaplan-Meier survival curves showing disease-specific mortality for whites and AA women diagnosed with vulvar cancer, by decade of diagnosis cohort and overall.

Kaplan-Meier survival curves showing disease-specific mortality for whites and AA women diagnosed with vulvar cancer, by decade of diagnosis cohort and overall

AA , African American; HR , hazard ratio.

Rauh-Hain. Racial disparities in vulvar cancer. Am J Obstet Gynecol 2013 .

Over the entire study period, after adjusting for race, SEER Registry, marital status, stage, age, treatment, grade, lymph node status, and decade, the AA race remained significantly associated with improved vulvar cancer related mortality compared with whites (HR, 0.66; 95% CI, 0.53–0.82). Table 2 presents the risk of mortality for AA compared with whites, stratified by decade of diagnosis. After adjusting for the same variables, there was a significant difference in vulvar cancer–specific mortality between AA and whites during the periods of 1990-1999 (HR, 0.62; 95% CI, 0.41–0.95) and 2000-2009 (HR, 0.46; 95% CI, 0.30–0.72), during which AA had a decreased risk of vulvar cancer–specific mortality. In contrast, after adjusting for the same variables, AA women had a higher HR of all-cause mortality during the period of 1980-1989 but not during the other decades.

Table 3 presents the risk of mortality patterns stratified by age group. In patients younger than 60 years old, after adjusting for the same variables, there was no difference in cancer-specific mortality in all the cohorts or all patients combined. In contrast, in patients 60 years old and older, AA had a decreased risk of vulvar cancer–specific mortality during the periods between 1990-1999 and 2000-2009 and all patients combined.

Survival analysis using the Cox proportional hazards model identified an independent association of older age, race, later stage, no treatment, and higher grade with higher mortality rates ( Table 4 ). The Cox model demonstrated that the strongest quantitative predictor of death was stage at the time of diagnosis, with more advanced stages having higher mortality rates. Treatment type was also significantly associated with mortality in this model; patients who underwent surgery had lower disease-specific mortality. In contrast, patients who received radiation had worse survival, even though stage was included in the model. The hazard of disease-specific mortality decreased over time in the periods of 1980-1989, 1990-1999, and 2000-2009 compared with the 1973-1979 cohort. Marriage was protective against all-cause mortality but not vulvar cancer–specific mortality. SEER site was not associated with all-cause mortality; however, Seattle, WA, had a significantly lower HR of disease-specific mortality compared with metropolitan Atlanta, GA.

Changes in disease characteristics and patterns of care over time were analyzed ( Table 5 ). Among white women, the mean age of diagnosis in each of the cohorts was between 65 and 69 years; in contrast, AA were diagnosed at a significantly younger age, a mean age between 56 and 59 years old in all the cohorts. There was not a significant difference in the rate of the different stages at diagnosis through the decades in AA or whites. There has been an increase in the rate of radiation in the most recent cohorts; compared with earlier cohorts, this has occurred in AA and whites.

Table 5

Patients with vulvar cancer stratified by race and date of diagnosis

Race	1970-1979			1980-1989			1990-1999			2000-2009
	14.0% (n = 819)			22.8% (n = 1339)			29.8% (n = 1751)			33.4% (n = 1958)
	White	AA	P value	White	AA	P value	White	AA	P value	White	AA	P value
n (%)	752 (91.8)	67 (8.2)	a	1257 (93.9)	82 (6.1)	a	1608 (91.8)	143 (8.2)	a	1762 (90.0)	196 (10.0)	a
Age at diagnosis, y			a			a			a			a
Mean	67.8	59		69	57.3		67.2	57.9		65.7	56.1
Median	71	58		72	56.5		71	57		66	53
Age group, y			a			a			a			a
<50	11.8%	26.9%		13.3%	34.1%		20%	39.2%		20.0%	35.2%
<60	14.0%	29.9%		12.2%	24.4%		11.1%	15.4%		19.0%	30.1%
<70	21.0%	19.4%		18.5%	11.0%		14.6%	16.1%		15.0%	16.8%
<80	31.6%	14.9%		28.5%	20.7%		27.1%	16.8%		20.1%	7.7%
≥80	21.5%	9.0%		27.6%	9.8%		27.1%	12.6%		25.8%	10.2%
Marital status at diagnosis, %			.07			.3			.001			a
Unmarried	55.5	65.7		56.7	59.8		54.3	66.4		54.7	67.9
Married	41.4	28.4		35.9	29.3		38.9	23.8		38.3	24.5
Unknown	3.2	6.0		7.4	11.0		6.8	9.8		7.0	7.7
Stage, %			.3			.006			.81			.88
Localized	66.0	62.7		62.9	57.3		62.4	58.7		61.1	61.2
Regional	23.7	28.4		26.1	23.2		28.3	30.1		33.0	32.7
Distant	3.2	6.0		4.5	13.4		3.4	4.2		3.7	4.6
Unstaged	7.2	3.0		6.4	6.1		5.9	7.0		2.2	1.5
Grade, %			.01			a			a			a
I	31.4	16.4		29.5	15.9		26.2	13.3		26.6	21.4
II	16.8	16.4		27.8	23.2		35.4	32.9		37	26
III	8.6	3		10.7	6.1		14.7	15.4		14	17.3
IV	0.7	1.5		0.4	3.7		0.6	0.7		0.3	0.5
Unknown	42.6	62.7		31.5	51.2		23.2	37.8		22.1	34.7
Surgery, %			.2			.009			.38			.85
None	10.9	14.9		8.5	18.3		11.6	15.4		12.9	13.3
Surgery	85.6	85.1		88.8	78		88.4	84.6		86.8	86.2
Unknown	3.5	0.0		2.7	3.7		0.1	0.0		0.3	0.5
Radiation, %			.38			.02			.07			.03
None	84.3	83.6		82.7	74.4		77.9	70.6		73.7	70.9
Radiation	14.6	13.4		15.9	20.7		21.2	27.3		25.8	27
Unknown	1.1	3.0		1.4	4.9		0.9	2.1		0.5	2.0

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