Which direction do nevus cells move? Abtropfung reexamined

Area of Science:

• Dermatology
• Histopathology
• Cell Biology

Background:

• Unna's 1893 Abtropfung theory proposed melanocytic nevus cells originate in the epidermis and descend into the dermis.
• This theory has been widely accepted, influencing the understanding of nevus development.
• Reassessment of this concept is crucial for accurate dermatological understanding.

Purpose of the Study:

• To critically evaluate Unna's Abtropfung theory using a large cohort of nevi.
• To investigate the developmental trajectory of melanocytic nevus cells.
• To compare the prevalence of different nevus types across age groups.

Main Methods:

• Histopathological analysis of 3,534 nevi from patients across all age demographics.
• Classification of nevi into junctional, compound, and dermal types.
• Statistical comparison of nevus distribution in different age cohorts.

Main Results:

• In children under 10, 48% had dermal nevi and 52% had compound nevi; no purely junctional nevi were observed.
• In individuals over 60, 65% had dermal nevi, 23% compound, and 12% junctional nevi.
• The observed distribution of nevus types across age groups does not support the Abtropfung theory.

Conclusions:

• The study's findings contradict Unna's Abtropfung theory.
• Data better align with a theory of upward migration of nevus cells.
• This research necessitates a re-evaluation of the established model for melanocytic nevus development.