Carcinoma In Situ.Care & specialists in Canada

Carcinoma in situ is the earliest stage of cancer. Malignant cells are confined to the layer of tissue where they began and have not invaded through the basement membrane into underlying tissue or blood vessels. Because of this, carcinoma in situ cannot spread to lymph nodes or distant organs. Five-year survival is above 95% across most sites with appropriate treatment.

Carcinoma in situ has the cytologic features of cancer (abnormal nuclei, disorganized growth, loss of normal architecture) but lacks the invasion through the basement membrane that defines truly invasive cancer. Most cancer staging systems classify CIS as stage 0 — present but not yet invasive. The diagnostic and prognostic implications differ substantially from invasive cancer.

Ductal carcinoma in situ (DCIS) is carcinoma in situ of the breast — malignant cells confined within the milk ducts without invasion of surrounding breast tissue. It accounts for 25-30% of newly diagnosed breast cancers and is usually detected by clustered microcalcifications on screening mammography. Treatment includes lumpectomy plus radiation, sometimes mastectomy, and endocrine therapy for hormone-receptor-positive disease.

Cervical intraepithelial neoplasia grade 3 (CIN3), also called high-grade squamous intraepithelial lesion (HSIL), is carcinoma in situ of the cervix. Persistent high-risk HPV infection drives full-thickness dysplastic change in cervical epithelium. Treatment is usually loop electrosurgical excision procedure (LEEP) or cold-knife conization, with cure rates above 90% with negative margins.

Bowen disease is squamous cell carcinoma in situ of the skin — a slowly enlarging red, scaly patch on chronically sun-exposed skin most often in adults over 60. Untreated, it progresses to invasive squamous cell carcinoma in 3-5% of cases. Treatments include topical 5-fluorouracil, topical imiquimod, photodynamic therapy, cryotherapy, and surgical excision, with clearance rates of 75-95%.

Carcinoma in situ of the bladder is a flat, high-grade lesion of the urothelium without papillary or invasive components. Often multifocal and frequently associated with smoking, it presents with urinary frequency, dysuria, or hematuria. Treatment is intravesical Bacillus Calmette-Guérin (BCG) for 1-3 years; radical cystectomy is reserved for BCG-refractory disease.

The risk depends on the site, grade, and treatment. Untreated CIN3 progresses to invasive cervical cancer in approximately 30% over 30 years. Untreated high-grade DCIS progresses to invasive breast cancer in 30-50%. Bowen disease progresses to invasive disease in 3-5%. Bladder CIS progresses to muscle-invasive disease in 30-80% over 5-10 years without treatment.

Diagnosis requires tissue biopsy with histopathology that confirms malignant cells confined to the epithelium without basement-membrane breach. The biopsy is taken from a lesion detected by screening — mammography for DCIS, cytology and HPV testing for CIN, skin examination for Bowen disease, cystoscopy for bladder CIS, endoscopy for esophageal high-grade dysplasia.

Most carcinoma in situ requires treatment because the risk of progression to invasive cancer is substantial. Active surveillance is being studied in low-risk DCIS through randomized trials (COMET, LORIS, LORD), with early data suggesting acceptable short-term safety. Outside trials, standard care for diagnosed CIS is treatment rather than observation.

Yes. Five-year survival exceeds 95% across most CIS sites with appropriate treatment. DCIS, CIN3, Bowen disease, bladder CIS, and high-grade Barrett dysplasia are all routinely cured by site-specific approaches. The main long-term concern is recurrence or new lesions in field-cancerized tissue, which is why surveillance after treatment is essential.

Five-year survival is above 95% across virtually all carcinoma in situ sites with appropriate treatment. Ten-year breast-cancer-specific mortality after treated DCIS is under 3%. Long-term mortality is driven mostly by subsequent invasive disease rather than the CIS itself, making adherence to surveillance and prevention strategies critical.

Major causes include persistent high-risk HPV (for cervical, anal, vulvar, oropharyngeal CIS), cumulative ultraviolet exposure (cutaneous CIS), tobacco and chemical carcinogens (bladder, oral, laryngeal CIS), chronic inflammation and metaplasia (Barrett esophagus, colon dysplasia), and inherited tumor-suppressor mutations such as BRCA1/2 and Lynch syndrome.

Recurrence is possible at the original site or as new lesions in field-cancerized tissue. Recurrence rates are 5-15% over 10 years for treated DCIS, 5-10% for treated CIN3, 10-20% for Bowen disease, and 30-40% for bladder CIS. Surveillance schedules — imaging, cytology, cystoscopy, or endoscopy — are designed to detect recurrences early.

Yes. HPV vaccination reduces incidence of high-grade cervical, anal, vulvar, and oropharyngeal intraepithelial neoplasia by over 80% in cohorts vaccinated before HPV exposure. Vaccination is also recommended after treatment of HPV-associated lesions, where observational data suggest lower recurrence rates.

Stage 0 is the AJCC stage assigned to carcinoma in situ across most cancer sites. It signifies that malignant cells are present but have not invaded beyond the epithelium. Five-year survival is above 95% for stage 0 disease, and treatment is local rather than systemic. Stage 0 is the most favorable cancer stage.

Most DCIS is treated with breast-conserving lumpectomy plus whole-breast radiation, with endocrine therapy added for hormone-receptor-positive disease. Mastectomy is used for extensive multifocal DCIS, contraindications to radiation, BRCA1/2 carriers, or patient preference. Sentinel lymph node biopsy is added when invasion is suspected at surgery.

Chemotherapy is generally not used for carcinoma in situ because the disease has not invaded blood vessels or lymphatics and cannot metastasize. Treatment is local — surgery, radiation, topical agents, intravesical therapy, or endoscopic resection. Endocrine therapy is used in hormone-receptor-positive DCIS as a chemopreventive measure rather than chemotherapy.

Bladder CIS is treated with intravesical Bacillus Calmette-Guérin (BCG) — a 6-week induction course followed by maintenance therapy for 1-3 years. Complete response is achieved in 65-75% at 3 months. Radical cystectomy is reserved for BCG-refractory or BCG-intolerant disease and extensive multifocal CIS.

There is currently no validated blood test for carcinoma in situ. Detection relies on site-specific screening: mammography for DCIS, cervical cytology and HPV testing for CIN, urinary cytology and cystoscopy for bladder CIS, skin examination for Bowen disease, and endoscopy for Barrett high-grade dysplasia. Blood-based multi-cancer early detection tests are an active research area but not yet validated for CIS.

Dysplasia refers to disordered cell growth with cytologic abnormalities of variable severity. High-grade or severe dysplasia is essentially synonymous with carcinoma in situ in many sites — the 2019 WHO classification formally equates high-grade dysplasia in Barrett esophagus, stomach, and colon with carcinoma in situ. Low-grade dysplasia is a milder precursor that may regress and does not require immediate treatment.