Incidence and Treatment Patterns of Pleomorphic Lobular Carcinoma in Situ: A Population-based Analysis After the Introduction of ICD-O-3 Code 8519/2.

INTRODUCTION

A dedicated morphology code (ICD-O-3 8519/2), introduced in 2018, made population-level description of PLCIS possible for the first time.

PATIENTS AND

METHODS

Women with lobular carcinoma in situ diagnosed during 2018 to 2023 were identified in the SEER 17-registry file; incidence came from the 21-registry file. Treatment was compared by logistic regression adjusted for age, race and ethnicity, and diagnosis year.

RESULTS

Of 11,170 women, 288 (2.6%) had PLCIS. Age-adjusted incidence was 0.08 per 100,000 woman-years (classic, 4.68), rising 8.7% annually and peaking at ages 65 to 69 rather than 50 to 54. Radiotherapy was given to 13.7% versus 1.2% of women treated by breast conservation (adjusted Odds Ratio [aOR], 10.96; 95% Confidence interval [CI], 6.84-17.09); receptor status was recorded in 64.2% versus 12.3% (aOR, 11.44), and 5.2% versus 17.8% had no recorded surgery (aOR, 0.24). Mastectomy differed little (23.3% vs. 20.8%; aOR, 1.27; 95% CI, 0.95-1.67). Findings were robust to age specification.

CONCLUSION

PLCIS is investigated and irradiated more intensively than classic disease; surgical extent differs little. Because the exposure relies on registrar transcription without central pathology review, and SEER cannot show why radiotherapy was given, these data describe practice rather than justify it. They do not support changing individual management, but call for prospective study recording central review, margin status and treatment indication.