Anus & perianal area
Carcinoma
Squamous cell carcinoma
Author: Raul S. Gonzalez, M.D.
Last author update: 31 March 2021
Last staff update: 13 March 2023 (update in progress)
Copyright: 2002-2023, PathologyOutlines.com, Inc.
PubMed Search: Squamous cell carcinoma [title] anus "free full text"[sb]
Table of Contents
Definition / general | Essential features | Terminology | Epidemiology | Pathophysiology | Clinical features | Prognostic factors | Treatment | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Sample pathology report | Differential diagnosis | Additional references | Board review style question #1 | Board review style answer #1Cite this page: Gonzalez RS. Squamous cell carcinoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/anusscc.html. Accessed March 22nd, 2023.
Definition / general
- Primary squamous cell carcinomas of anus
Essential features
- Most common carcinoma of anal tract
- Increasing in incidence, although still relatively rare (incidence of < 1 per 100,000)
- Can arise either above or below dentate line
Terminology
- WHO officially only recognizes squamous cell carcinoma
- Basaloid variant has also been termed cloacogenic or transitional
- Mucoepidermoid carcinoma may be used for tumors with prominent mucinous features, although the biology may be different (J Gastroenterol 2001;36:508)
Epidemiology
- Tumors above dentate line: more common in women, usually diagnosed in sixth decade
- Tumors below dentate line: more common in men, usually diagnosed in third decade
Pathophysiology
- Tumors below dentate line usually have an associated finding (condyloma, fistula, radiation, etc.)
- Can be caused by high risk HPV (Cancer Res 1999;59:753)
- EGFR overexpression is common (Mod Pathol 2006;19:942)
Clinical features
- Presenting symptoms include rectal bleeding, pain, mass
Prognostic factors
- Prognosis depends on AJCC stage of tumor
- Distal tumors have better prognosis (slower growth, earlier detection)
- Better prognosis if higher radiation dose and no / shorter treatment interruptions (Gastrointest Cancer Res 2008;2:10)
- Worse prognosis if older or male or with HIV (Dis Colon Rectum 2009;52:624, Dis Colon Rectum 2001;44:1496)
Treatment
- Surgery with chemoradiation
Gross description
- Anal canal tumors are nodular, ulcerated, 3 - 4 cm or more
- Invade deeply into wall and spread proximally and distally into submucosa of distal rectum and proximal anus
Microscopic (histologic) description
- Resembles squamous cell carcinoma as seen elsewhere in body
- Tumors often display multiple morphologic patterns, calling into question the utility of subdividing the entity
- May be keratinizing (usually below the dentate line) or nonkeratinizing (anywhere, although tumors above dentate line are usually nonkeratinizing)
- Basaloid subtype shows plexiform pattern and palisading of small undifferentiated cells around the border, with central necrosis of tumor nodules (also mitotic figures, invasion, desmoplastic stroma)
- May have massive eosinophilic infiltration, mucoepidermoid features (with mucinous microcysts) or poorly differentiated morphology
- Can show "small cell" anaplastic features (but without evidence of neuroendocrine differentiation)
- Often replaces crypts of adjacent rectal mucosa
- May show overlying / adjacent dysplastic changes (anal intraepithelial neoplasia)
Microscopic (histologic) images
Contributed by Raul S. Gonzalez, M.D.
Squamous cell carcinoma
Sample pathology report
- Anus, mass, biopsy:
- Focal invasive squamous cell carcinoma, arising in a background of high grade squamous intraepithelial lesion (AIN 3)
- Anus, resection:
- Squamous cell carcinoma, moderately differentiated (see synoptic report)
Differential diagnosis
- Basal cell carcinoma:
- Fewer mitotic figures, smaller cells, retraction artifact
- Small cell carcinoma:
- Can resemble basaloid squamous cell carcinoma but expresses neuroendocrine markers
- Verrucous carcinoma:
- Grows in an exophytic, not infiltrative, pattern
Additional references
Board review style question #1
- Which of the following is true about anal squamous cell carcinoma?
- Cases above the dentate line are more common in men
- Cases below the dentate line are more common in elderly patients
- Patients with HIV have a worse prognosis
- Vast majority are purely basaloid
Board review style answer #1
