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

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. 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). 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). 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.