Frequency of naevus cells in lymph nodes of melanoma and breast cancer patients

Introduction: We aimed to study the frequency (prevalence) and histology of benign melanocytic naevus cells in regional lymph nodes in relation to age and sex and nodal location. Material and methods: Histopathology reports of sentinel lymph node (SLN) biopsies from melanoma patients, 2002 - 2014, and from breast cancer patients, 2010- 2019, were obtained from records of a single hospital in England. All sections were similarly processed and examined. For standardisation, presence of naevus cells was assessed in a single node per patient: the first SLN biopsied (melanoma) or the node nearest the first SLN (breast cancer). Results: Associations were tested using Fisher's exact test. Naevus cells were found in 10% (60/585) of melanoma patients' index SLNs. Frequency varied significantly by anatomic region: 13% in axillary to 0% cervical SLNs (p = 0.03), but not by sex or age. Within nodes, naevus cells were present in capsular or pericapsular tissue (93%), or trabeculae (7%). In breast cancer patients' index axillary nodes, 6% (11/196) contained naevus cells, all intracapsular. In the predominant 40-69 years age-group, prevalence was similar in breast cancer (7%) and female melanoma (9%) patients, but in those aged 70-100, prevalence was lower in breast cancer (2%) than in female melanoma (15%) patients (p = 0.05). Conclusions: Standard methods of assessment yielded no clear pattern of naevus cell frequency in lymph nodes by age or sex, but confirmed naevus cell location as mostly intracapsular.