Gastrointestinal stromal tumour of the anorectum

CD117

96/96

CD34

84/89(this is a higher rate than at other sites)

SMA

7/87(of which 6 cases were CD34 positive)

Desmin

1/80

S-100

0/80

Cytokeratin 18 (clone DC-10)

2/57

GFAP

0/53

Neurofilament

0/57

Smooth muscle tumours

SMA and desmin positive. Most are CD34 and CD117 negative

Endometrial stromal sarcoma arising in endometriosis or spreading from the uterus

CD10 and hormone receptor positive

Schwannoma

very rare in rectum. S-100 positive. CD34 and CD117 negative.

Melanoma

S-100 and HMB-45 positive. May be CD117 positive

<2 cm or less in diameter and <= 5 mitoses/50 HPF

indolent; 1 of 20 had a recurrence and none had metastases

2 to 5 cm diameter and <= 5 mitoses/50 HPF

2 of 12 had recurrences plus one died of tumour

5 cm or larger OR more than five mitoses per 50 HPFs

malignant behaviour; 56/73 had recurrence, metastases or died of disease