Table 2 Explaining non-linear stage group mappings between the three staging systems

Melanoma

- T2b N0 M0 derives to AJCC-SG II and, by simplified business rules which do not substage, to RD-stage I.

- Any T with N0 M0 maps to DoS 1 (rarely 2) and either a RD-stage/AJCC-SG I or II depending on the T value assigned.

- In NSWCR, DoS 2 (in the absence of regional lymph node metastasis) has conventionally been assigned to: (i) a primary cutaneous melanoma involving subcutaneous fat (Clark’s level V) which could potentially map to AJCC-SG/RD-stage I or II (most likely II) and (ii) a primary cutaneous melanoma with satellite nodules/in-transit nodules, which equates to N2c in AJCC staging (pathological AJCC-SG IIIBor IIIC and RD-stage III).

Prostate

- PSA and Gleason scores are not factored into the algorithms for deriving AJCC-SG in NSWCR.

- VicCR business rules assign RD-stage I for cases either (i) without a PSA or Gleason score or (ii) both PSA < 10 and Gleason score ≤ 6. RD-stage II is assigned for cases where (i) PSA ≥10 or (ii) Gleason score > 7. Given the poor availability of PSA data in PBCRs generally, there is a tendency for down-staging of prostate cancer in NSWCR by both AJCC and RD-staging systems.

- In NSWCR, a DoS cannot be assigned by a coder based on a core biopsy or transurethral resection of the prostate (TURP) unless there is a clear description of extraprostatic extension, in which case DoS 2 can be assigned. However, a DoS may be recorded in an associated electronic notification. This compares to AJCC-TNM and RD-staging, in which prostate cancer in a core biopsy or TURP alone can be assigned a T value and allocated to stages I or II, depending on the PSA and/or Gleason score.

- In NSWCR, where PSA and/or Gleason score are unknown, a core biopsy diagnosis of prostate cancer would derive to AJCC-SG/RD-stage I.

- In NSWCR, DoS 1 can be assigned when a prostatectomy shows cancer localised to the prostate; these cases correspond to T2 tumours = AJCC-SG and RD-stage II (and occasionally I).

- In NSWCR, the majority of cases with DoS 2 would reflect cases for which a prostatectomy was performed and there was evidence of extraprostatic extension; these cases correspond to T3 tumours (AJCC-SG and RD-stage III).

- Cases staged as T4 N0 M0 equate to DoS 2 but AJCC-SG/RD-stage IV.

- Cases staged as any T with N1 M0 equate to DoS 3 in NSWCR, but AJCC-SG/RD-stage IV.

Colorectal

- Colorectal tumour extending beyond the muscle coat into subserosa only is assigned DoS 1, whereas these would likely be staged as pT3 (AJCC-SG/RD-stage II).

Breast

- An invasive tumour of any size localised to the breast would be assigned DoS 1.

- DoS 2 would be assigned by a coder if there was skin, nipple (associated Paget disease), or chest wall involvement (effectively T4 tumours).

- Any lymph node involvement other than isolated tumour cells alone is assigned DoS 3.

Lung

- Tumours staged as T2b N0 M0 (AJCC-SG IIA) would simplify to RD-stage I as the VicCR business rules do not substage T2 tumours.

- Lung tumours that invade pleura or immediate adjacent tissues or organs are assigned DoS 2 by NSWCR coders irrespective of tumour size, so a DoS 2 tumour could be equivalent to a T1-T4 tumour in AJCC-TNM staging. Therefore, in the absence of regional lymph node involvement, these tumours could be staged as AJCC-SG/RD-stage I, II, or III.

- The presence of a malignant pleural effusion has been variably interpreted by NSWCR and hospital coders as DoS 2 or DoS 4, although mainly as DoS 4, which equates to M1a (AJCC and RD-stage IV).