Especially as one deals with staging issues in malignancy, there is a very real possibility of "over-staging" or "up-staging" in a false-positive fashion if the pathologist is not alert to the issue of rests and ectopic tissues. Primary malignancies may arise from rests. These things REALLY exist & have the potential to cause problems!

• Carcinoma staging:
  • embryonic cell rests, examples:
    • LMC-92-651 = a 1 by 2 mm adrenal rest in hernia sac of 16 month old male
    • L07-6760 = left axillary mass SCC & node primary anywhere.
    • L10-6215 = seminoma radical orchiectomy barely into rete & a 5mm nodule found at proximal resection margin (an adrenal rest...nuclei of cells clearly benignly different from the seminoma).
    • L10-6050 = breast cancer with two negative SLNs but an IHC positive focus noted just outside one (salivary gland rest...H&E clearly benignly different from the cancer).
  • biopsy or surgically dislodged gland fragments, examples:
    • breast case: we had at least one in 2009 that was not ca because not the large grade III cells of the primary.
  • fat necrosis: with some pseudo-epithelial clusters (solved with IHCs & we had a case in 2010).
• Melanoma staging:
  • node capsule nevus, examples: a primary melanoma from one [L08-3623].
• Carcinomatous node & no history of previous primary:
  • merkle cell ca. (L10-3010, as a 6.8 CM left axillary mass in 57 y/o male ck20 positive with perinuclear dot pattern & neuroendocrine marker pos.)

(began posting 18 July 2010; latest addition 2 January 2011)