Pap Smear Screening for Women on Tamoxifen
Women taking tamoxifen should follow standard cervical cancer screening guidelines for their age group—tamoxifen does not require annual Pap smears, but does require annual gynecologic assessment focused on endometrial surveillance.
Standard Cervical Cancer Screening Applies
The most authoritative guideline addressing this question is the 2016 American Cancer Society/American Society of Clinical Oncology Breast Cancer Survivorship Care Guideline, which explicitly states that primary care clinicians should screen for other cancers, as they would for patients in the general population 1. This means:
- Women ages 21-29: Pap test every 3 years 1
- Women ages 30-65: Either HPV co-testing with Pap test every 5 years (preferred) OR Pap test alone every 3 years 1
- Women over age 65: Discontinue screening if they have had 3 consecutive negative Pap tests or 2 consecutive negative HPV and Pap tests within the last 10 years, with the most recent test occurring within the last 5 years 1, 2
What IS Required Annually: Gynecologic Assessment
The critical distinction is that while Pap smears follow standard intervals, postmenopausal women on selective estrogen receptor modulators (SERMs) like tamoxifen require an annual gynecologic assessment 1. This assessment focuses on:
- Symptom surveillance: Patients must be counseled to immediately report any vaginal spotting or bleeding, as tamoxifen increases endometrial cancer risk in postmenopausal women 1, 3
- Clinical pelvic examination: Annual gynecologic examination to assess for abnormal findings 1
- Endometrial monitoring: The FDA label confirms that patients receiving tamoxifen should have annual gynecological examinations and promptly report abnormal gynecological symptoms including menstrual irregularities, abnormal vaginal bleeding, changes in vaginal discharge, or pelvic pain or pressure 3
Why Tamoxifen Doesn't Change Cervical Screening
Research demonstrates that tamoxifen may cause benign squamous atypia in cervical smears, but this is not associated with increased cervical intraepithelial lesions or cervical cancer 4. A study of 52 breast cancer patients on tamoxifen showed that while 55-78% had cytologic atypias, subsequent cervical biopsies in 13 patients with ASCUS findings revealed no dysplasia or HPV changes 4. The concern with tamoxifen is endometrial, not cervical 3, 5.
Common Pitfalls to Avoid
- Do not order annual Pap smears simply because a patient is on tamoxifen—this represents over-screening without evidence of benefit 1
- Do not skip the annual gynecologic assessment—this is where endometrial surveillance occurs and is specifically recommended for tamoxifen users 1, 3
- Do not perform routine endometrial sampling in asymptomatic women on tamoxifen, as data from the NSABP P-1 trial showed this did not alter endometrial cancer detection rates (0.6% with sampling vs 0.5% without) 3
- Do educate patients that any abnormal vaginal bleeding requires prompt evaluation, as 29 of 33 endometrial cancers in the NSABP P-1 trial were diagnosed in symptomatic women 3
Special Considerations
If the patient has never been adequately screened for cervical cancer, she should receive at least 2 negative Pap smears 1 year apart regardless of age before transitioning to standard intervals 2. Women with prior high-grade cervical lesions (CIN2+) require continued screening for at least 20 years after treatment, even if this extends past age 65 2, 6.