From ff725218cdd0dc9d46977ec340cc22a7163733f2 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <61934744+phofl@users.noreply.github.com>
Date: Tue, 20 Feb 2024 18:26:52 +0100
Subject: [PATCH] Backport PR #57489: REGR: astype introducing decimals when
 casting from int with na to string

---
 doc/source/whatsnew/v2.2.1.rst             | 1 +
 pandas/_libs/lib.pyx                       | 2 +-
 pandas/tests/series/methods/test_astype.py | 8 ++++++++
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v2.2.1.rst b/doc/source/whatsnew/v2.2.1.rst
index 6c6a37b2b2f89..85b9346aa01a5 100644
--- a/doc/source/whatsnew/v2.2.1.rst
+++ b/doc/source/whatsnew/v2.2.1.rst
@@ -39,6 +39,7 @@ Fixed regressions
 - Fixed regression in :meth:`DataFrameGroupBy.idxmin`, :meth:`DataFrameGroupBy.idxmax`, :meth:`SeriesGroupBy.idxmin`, :meth:`SeriesGroupBy.idxmax` where values containing the minimum or maximum value for the dtype could produce incorrect results (:issue:`57040`)
 - Fixed regression in :meth:`ExtensionArray.to_numpy` raising for non-numeric masked dtypes (:issue:`56991`)
 - Fixed regression in :meth:`Index.join` raising ``TypeError`` when joining an empty index to a non-empty index containing mixed dtype values (:issue:`57048`)
+- Fixed regression in :meth:`Series.astype` introducing decimals when converting from integer with missing values to string dtype (:issue:`57418`)
 - Fixed regression in :meth:`Series.pct_change` raising a ``ValueError`` for an empty :class:`Series` (:issue:`57056`)
 - Fixed regression in :meth:`Series.to_numpy` when dtype is given as float and the data contains NaNs (:issue:`57121`)
 
diff --git a/pandas/_libs/lib.pyx b/pandas/_libs/lib.pyx
index c483f35513a40..7656e8d986117 100644
--- a/pandas/_libs/lib.pyx
+++ b/pandas/_libs/lib.pyx
@@ -759,7 +759,7 @@ cpdef ndarray[object] ensure_string_array(
             out = arr.astype(str).astype(object)
             out[arr.isna()] = na_value
             return out
-        arr = arr.to_numpy()
+        arr = arr.to_numpy(dtype=object)
     elif not util.is_array(arr):
         arr = np.array(arr, dtype="object")
 
diff --git a/pandas/tests/series/methods/test_astype.py b/pandas/tests/series/methods/test_astype.py
index 46f55fff91e41..4c8028e74ee55 100644
--- a/pandas/tests/series/methods/test_astype.py
+++ b/pandas/tests/series/methods/test_astype.py
@@ -673,3 +673,11 @@ def test_astype_timedelta64_with_np_nan(self):
         result = Series([Timedelta(1), np.nan], dtype="timedelta64[ns]")
         expected = Series([Timedelta(1), NaT], dtype="timedelta64[ns]")
         tm.assert_series_equal(result, expected)
+
+    @td.skip_if_no("pyarrow")
+    def test_astype_int_na_string(self):
+        # GH#57418
+        ser = Series([12, NA], dtype="Int64[pyarrow]")
+        result = ser.astype("string[pyarrow]")
+        expected = Series(["12", NA], dtype="string[pyarrow]")
+        tm.assert_series_equal(result, expected)