Percentages of unstaged disease increased significantly with age for each of the 18 selected cancer sites, as consistent with previous studies [1
]. Age and comorbid conditions limit one's ability to undergo testing and examinations. Neither elderly patients nor their family members may consent to a diagnostic workup [3
]. This is especially the case when older patients have competing health problems that limit disease investigation. In a study involving elderly postmenopausal breast cancer patients, the authors concluded that compromised health status associated with age may have precluded patients from obtaining certain prognostic information (e.g., Axillary lymph node dissection [AxLND] for breast cancer patients), which in turn can limit treatment options [1
Married individuals were significantly more likely to receive a cancer staging, after adjusting for age, sex, and race. Previous studies have not specifically considered the influence of marital status on unknown stage. However, this result is consistent with findings from studies showing that married cancer patients tend to be identified at an earlier stage of disease, experience fewer comorbid conditions, and have better prognosis [14
]. One study reported that married individuals have higher socioeconomic status and social support, which in turn leads to higher survival than non-married individuals [17
]. Older women who are assigned an advanced tumor stage or no tumor stage at diagnosis are more likely to be widowed than younger women, who will also have a higher chance of survival. Another study found that women who were married, white or of higher socioeconomic status were more likely to undergo mammography and receive pap testing than single women [16
]. Married women enjoy the benefit of a combined income and a stable partner, which increases their likelihood of being able to afford appropriate medical services.
The higher percentage of unstaged cases who are of Spanish-Hispanic-Latino descent or who reside in Appalachia may be explained, at least in part, by lower levels of health insurance, which limits one's ability to undergo testing and examinations. Culture may also influence the patient's willingness to consent to a diagnostic workup. In addition, a thorough cancer workup is more limited among patients of poorer overall health status. Further research focusing on cancer staging by ethnicity and Appalachia status is warranted.
The percentage of cases receiving an unknown stage assignment decreased over the study period for 15 of the 18 cancer sites considered. Other studies focusing on colon and rectal cancers and prostate cancer also observed a decrease in unknown staging [2
]. Reasons for this increase in staging may include physician education, introduction of less invasive staging procedures, and adoption of a collaborative staging system by SEER in 2004, which combines and standardizes information using computer algorithms to assign a stage.
This study also revealed a higher percentage of unstaged rectal cancer than colon cancer. The authors of another study likewise observed a higher percentage of unstaged rectal cancer than colon cancer, attributing this to the limited availability of endoscopic ultrasounds often required for staging rectal cancer [2
]. However, the same screening methods are typically used to detect both rectal and colon cancer, and some of these methods (e.g., sigmoidoscopy) are more likely to detect cancers of the rectum or distal colon.
Two previous SEER data-based studies identified that the percentage of unstaged colorectal cancer was significantly lower for males than females [3
]. In the current study, we found no significant difference in the percentage of unstaged colon or rectal cancers between males and females, after adjusting for age and race. However, in rerunning the models without adjusting for these variables, a similar result was found to those in the previous studies. The large difference in life expectancy between males and females in the U.S. emphasizes the need to adjust for the potential confounding effect of age. In addition, some researchers have identified that older males in the U.S. tend to have higher socioeconomic status than their female counterparts, and that older women are more likely to be insured by Medicaid [3
]. Patients with advanced age and covered by Medicaid have a higher probability of having their cancer recorded as unknown.
Lower screening rates among females for esophageal and stomach cancers may explain significantly higher rates of unstaged disease for females compared to males after adjusting for age and race. For example, one study involving stomach cancer reported that 32.5% of men compared with 23.5% of women underwent screening for the disease [18
]. Of those who were screened, approximately half were screened at work, which suggests that unemployed women are less likely to be screened. (Note that in the U.S., only high risk individuals are recommended to pursue esophageal or stomach cancer screening [19
].) Also, because stomach cancer is more prevalent among males than females, females are less motivated to undergo screening for this disease--especially since no routine stomach cancer screening method exists [19
Black males were less likely than white males to be assigned a tumor stage for cancers involving the stomach, rectum, colon, kidney and renal pelvis, and thyroid. Black females were less likely than white females to be assigned a tumor stage for cancers involving the breast, corpus, cervix, and ovaries. Higher levels of unstaged disease among blacks have been observed in other studies [4
]. A higher level of unstaged disease among blacks compared with whites is consistent with their tendency to be diagnosed at a later stage, to have more comorbid conditions, and to experience poorer survival rates [20
]. Poorer survival among unstaged patients may be explained by lower levels of treatment [1
] In addition, unstaged patients who do not receive surgery tend to experience more severe comorbidities than patients that receive treatment [1
]. Although unstaged disease influences treatment outcomes, age and comorbid conditions are contributing factors since they are negatively associated with cancer-directed therapy [5
One study found that uninsured patients are less likely to receive a tumor stage than insured patients [6
]. Another study observed that poorer socioeconomic status among blacks is associated with generally more advanced cancers of the colon or rectum, lung, and cervix [23
], which in turn could explain higher levels of unstaged disease [5
]. Lower socioeconomic status is likely associated with blacks seeking medical care later in the disease process, which in turn influences their higher levels of unstaged disease. With a greater proportion of unstaged disease among minorities, race-stage information may be biased.
Only for white females were the cancer sites with higher incidence rates significantly associated with lower unstaged disease. This may be because of increased cost associated with rare cancer diagnosis and treatment [24
]. Individuals with rare cancers will probably need more sophisticated diagnostic procedures in general, and those who refuse such procedures because of age or monetary factors will be more likely to receive an unknown tumor stage diagnosis.
We observed a strong and consistent association between cancer sites with better survival having lower unstaged disease. For patients with poor prognosis, cancer staging may not be necessary. On the other hand, not receiving a tumor stage may result in not receiving life extending treatment.
Strengths and weaknesses of the SEER data need some consideration. Cancer registries in the SEER Program incorporate several quality assurance measures, identify nearly all diagnosed cases in their catchment areas, and have a very high level of follow-up for vital status. Criteria used by SEER regarding formatting and defining case information are described elsewhere [25
]. SEER data provide a large number of cases with detailed information on patient demographics, tumor characteristics, morphology, diagnostic information, and extent of disease. This allowed us to adjust for selected factors while assessing unstaged disease. In addition, the 17 SEER registries included in this study cover approximately 26% of the U.S., with both urban and rural areas represented. Hence, the results have a high level of external validity. One study found that the SEER coverage area may under represent tobacco-related cancers [27
]. While SEER does not collect data on comorbid diseases for conditions other than cancer, relative survival provided us with a measure of net survival (survival in the absence of other causes).