Besides classical adenocarcinoma (AC), mucinous adenocarcinoma (MAC) and signet-ring cell carcinoma (SRCC) are less frequent subtypes of colorectal cancer, and their recent epidemiologic data are lacking. The current study was designed to explore the evolving epidemiology and prognosis of patients with colorectal MAC and SRCC, compared with AC.
The Surveillance, Epidemiology and End Results (SEER) registry database was adopted for patients with pathologically confirmed colorectal neoplasms as their first malignancy. Incidence and survival trends were estimated by age and histologic subtype. 5-year cancer specific survival (CSS) were evaluated for entire cohort, and compared in subgroups by age, grade and stage. Multivariate analysis of CSS was conducted for entire cohort.
MAC incidence (per 100,000) declined slightly from 6.1 in 1975 to 5.6 in 2001, and fell to 2.5 in 2012 with an APC of -7.8% (95%CI=-8.8%–6.8%, P < 0.001), then reached a plateau. SRCC incidence gradually climbed from 0.1 in 1975 to 0.6 in 1999 with an APC of 8.3% (95%CI=7.2%-9.4%, P < 0.001) and went down to 0.4 in 2014 with an APC of -3.0% (95%CI=-5.0%–1.0%, P < 0.001). Among patients younger than age 50 years, MAC incidence decreased at an APC of -2.6% (95%CI: -3.6%–1.6%, P < 0.001), and SRCC remained stable, whereas AC incidence increased greatly at an APC of 1.9% (95%CI: 1.6%-2.2%, P < 0.001). Survival of both MAC and AC increased over time, while the survival of SRCC fluctuated without evident improvement. The 5-year CSS of SRCC was 31.3%, significantly lower than AC (66.6%) and MAC (60.4%). For AC and MAC Survival rate of patients aged below 50 years was superior to those aged 50 years or over through time, while in SRCC, after follow-up of approximately 20 months, the survival rate of younger patients dropped and became lower than older patients. Histologic subtype was an independent factor for CSS of CRC.
The incidence and survival of colorectal MAC and SRCC differs from traditional AC. Despite of the low incidence of SRCC, the survival is significantly worse than AC and MAC, especially for patients aged younger than 50 years. Further studies of the etiologies and treatment for rare subtypes of CRC are needed.
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The author has declared no conflicts of interest.