Clinicians could catch more tiny melanomas with comprehensive imaging than with dermoscopy, Australian dermatologists say after finding the latter method may miss up to 50% of lesions smaller than 5mm.

A study of 312 consecutively-diagnosed primary melanomas found the dermoscopic seven-point and three-point checklists would have missed 48% and 49% of the 86 ≤5 mm melanomas identified with dermoscopy, total body photography (TBP) and sequential digital dermoscopy imaging (SDDI).  The Menzies’ method and revised pattern analysis weren’t much better, correctly identifying 66% and 64% of tiny lesions.

Tiny melanomas were most frequently detected when new or changing and positively identified based on asymmetrical structure or colour, brown dots, irregular dots and globules and atypical pigment networks, Sydney Melanoma Diagnostic Centre consultant dermatologist and clinical researcher Dr Amanda Pereira and her team wrote in Clinical and Experimental Dermatology.

Invasive lesions, which constituted 44% of tiny melanomas, often had atypical vascular patterns, shiny white lines and grey/blue structures on dermoscopy. The features were associated with dermal malignant cells, regression, fibrosis and inflammation and “should prompt excision” rather than monitoring, they advised.

Despite previous studies finding positive correlations between diameter and tumour thickness, “there is growing evidence demonstrating that small does not mean in situ, with up to 70% of these lesions reported as being invasive”, they wrote.

They also “represent a diagnostic pitfall”, with incomplete development of specific melanoma features and subjectivity in some dermoscopic criteria potentially hindering recognition.

“In some cases, the only clue may be evidence of a new or changing lesion based on [TBP and SDDI],” they wrote.

Clinician expectations may also affect detection “with more amelanotic and light-coloured melanomas expected in Australian patients”, they noted.

While most invasive tiny melanomas in this study were stage 1 and would have had less impact on morbidity, mortality and healthcare costs than more advanced lesions, failure to detect and remove them until they’ve reached the proposed 6 mm biopsy threshold could put patients at increased risk of locoregional or distant metastasis and expose them to larger excision wounds.

The study highlights the importance of early detection and TBP and SDDI’s role in facilitating that, the authors wrote.

“Incomplete development of specific melanoma features on dermoscopy may lead to suboptimal diagnostic accuracy and therefore early diagnosis frequently relies on the detection of a new and changing lesion aided by TBP and SDDI,” they concluded.